Frater duas conchas in sporta ponit, sed soror dicit unam pulchriorem esse.

Because duas conchas is the direct object of ponit (puts).

• duas = two, feminine accusative plural
• conchas = shells, feminine accusative plural

Since the brother is putting the shells somewhere, the shells are the things being acted on, so Latin uses the accusative case.

If shells were the subject, you would expect something like duae conchae, not duas conchas.

Because in can take either the ablative or the accusative, depending on the meaning.

• in + ablative = in / on a place, showing location
• in + accusative = into / onto a place, showing motion toward

Here, in sporta literally means in the basket. In many beginner sentences with ponit, English uses into, but Latin often still focuses on the resulting location: the shells end up in the basket.

So:

• in sporta = in the basket
• in sportam would more strongly emphasize movement into the basket

Because after verbs of saying, thinking, knowing, and perceiving, Latin very often uses an indirect statement construction.

That construction is:

• accusative subject
• infinitive verb

So in soror dicit unam pulchriorem esse:

• unam is the subject of the infinitive, in the accusative
• esse is the infinitive to be

Literally, it is something like:

• the sister says one to be prettier

Natural English makes this:

• the sister says that one is prettier

This is one of the most important Latin constructions to learn.

unam means one, specifically one of the two shells.

It is feminine accusative singular, because it stands for an understood noun like concham:

• unam (concham) = one shell

Latin often leaves out a noun when it is obvious from context. Since the sentence has already mentioned duas conchas, unam naturally means one of them.

pulchriorem is the comparative form of pulcher (beautiful).

So:

• pulcher = beautiful
• pulchrior = more beautiful / prettier
• pulchriorem = prettier, in the accusative singular feminine (or masculine)

It matches unam in case, number, and gender, because it describes that understood concham.

So:

• unam pulchriorem = one [shell] prettier

Latin comparatives do not always need an explicit than phrase.

Here, unam pulchriorem esse naturally means:

• one is prettier
• that is, one is prettier than the other

Since there are only two shells in the context, the comparison is obvious.

Latin can also make the comparison explicit with quam, but it does not have to. The sentence is perfectly natural as it stands.

The subject of esse is unam.

This can feel strange to an English speaker, because in English the subject of is would be nominative: one is prettier.

But in Latin indirect statement, the subject goes into the accusative, not the nominative. So:

• unam = subject of esse
• esse = infinitive to be

That is why you do not see una here.

Because unam is not the main subject of the whole sentence. The main subject of the whole second clause is soror.

Inside the indirect statement after dicit, the subject is put into the accusative. So Latin uses:

• unam = accusative singular feminine

If it were the subject of a normal main clause, then you would get una:

• una pulchrior est = one is prettier

But after dicit, Latin switches to the accusative-and-infinitive pattern:

• dicit unam pulchriorem esse

In this kind of indirect statement, esse is normally expressed.

So:

• dicit unam pulchriorem esse = she says that one is prettier

In some kinds of Latin writing, especially poetry or very compressed prose, forms of to be can sometimes be omitted, but for normal beginner prose you should expect esse to be there.

Latin word order is much more flexible than English word order because Latin uses endings to show grammatical relationships.

So English needs word order more strictly:

• The brother puts two shells in the basket

Latin can move words around more freely because:

• frater is clearly nominative
• duas conchas is clearly accusative
• in sporta is clearly a prepositional phrase
• ponit is clearly the verb

Putting ponit at the end is very common in Latin. Likewise, placing unam pulchriorem esse after dicit is normal Latin style.

Latin has no articles.

So a word like frater can mean:

• brother
• a brother
• the brother

And soror can mean:

• sister
• a sister
• the sister

You decide from context what sounds best in English.

Here are the main forms:

• frater, fratris = brother
• duo, duae, duo = two
• concha, conchae = shell
• sporta, sportae = basket
• pono, ponere, posui, positum = put, place
• sed = but
• soror, sororis = sister
• dico, dicere, dixi, dictum = say
• unus, una, unum = one
• pulcher, pulchra, pulchrum = beautiful
• sum, esse, fui = be

Seeing the dictionary forms helps explain the endings you see in the sentence.

Yes. In the comparative, the accusative singular masculine and feminine have the same form:

• masculine accusative singular: pulchriorem
• feminine accusative singular: pulchriorem

So here it is feminine because it agrees with unam, which stands for one shell.

That sameness is normal for comparatives.

No. pulchriorem is definitely a comparative form, so it means:

• more beautiful
• prettier

It is not just a stronger form of beautiful. The idea of comparison is built into the ending.

So the sense is that one shell is being judged more beautiful than another.