CRUSTACEA. 
237 
the body ; and he explains the differentiation which takes place 
in the parts of the appendages in the structure of the mouth of 
Crustacea, as well as in the Insecta. 
6. The prehensile mouths in Crustacea exhibit three types, 
which he illustrates in pi. x. : — 1st, in Oniscus, Asellus, Idotea, 
and Sphcuroma. 
7. 2nd in which he considers to be the highest de- 
veloped Isopoda. 
8. 3rd in Serolis, 
9. The author epitomizes the characters distinguishing the 
three different types. 
10. He describes the sucking-mouth of the Cymothoidce, which 
he illustrates in pi. xi., taking as typical forms those of AS,ga 
psora (L.) and Cymothoa oestrum (auct.), which he compares 
with that of Anilocra leachii (Kroy.) , a new species, as also with 
that of one taken by Kroyer on some fish in the river Plate, 
and which forms the type of a new genus, Artystone^ the cha- 
racters of Avhich arc given further on in this llccord. 
11. Ex])lains how the different parts of the mouth of Cymothoa 
are formed into sucking-instruments. 
12. The author gives a long description of the mouth of AEga. 
13. He gives a concise account of the mouth of Cymothoa. 
14. On the structure of the intestinal region of Ciymothoa, and 
some superstitions of the Icelanders and ancients in relation to 
these creatures. 
15. The author gives a description of the larva of Cymothoa 
oestrum when it is first excluded from the ovisac, which, as it has 
not been previously described, we give here in full : — 
When ‘tlie young Cymothoa oestrum quits the ovisac, it has a 
sharp frontal edge, Avelf developed, oblong, projecting black eyes, 
slender bristle-like antennse, the posterior pair being so long 
that they reach to the middle of the pleon. It has the pereiopoda 
slender, with long claws, curved at the extremity only ; the three 
anterior pairs, directed forwards, are serrated along the under 
surface. Picon quite free, and scarcely shorter than the pereion, 
cone-formed, with freely moving somites. Pleopoda furnished with 
long plumose cilia, the posterior pair nearly as long as the five 
anterior somites of the pleon, furnished at the extremity with 
long plumose cilia. The posterior pair of pereiopoda, as in 
many of the larvDe of the Isopoda in their earliest condition, are 
wanting. 
The author concludes with some remarks on the classification 
of tliesc Crustacea, which cannot, he thinks, be satisfactorily de- 
termined until the oral organs be properly understood. 
Serolis orhiynyana (Milne-Edw.), Scliiodte, 1. c. p. 204, tab. x. fig. 2. 
Cymothoa (cstrum (L.), Heller, Verliandl. d. zool.-bot. Gesell, in Wien, 
p. 739. — C. cestroidcs, Heller, 1. c. p. 737. — C. paralleJa (Otto), Heller, 1. c. 
p. 738. — C. amlouini (Edw.), Heller, 1. c. p. 738. 
