32 NEW-YORK FAUNA — CRUSTACEA. 
This is abundant in winter on our coast. It is called Opossum Shrimp in England, from 
the circumstance that it carries a sac under the thorax, in which the eggs are hatched, and 
where they are carried for some time. It is supposed by more recent writers to be the males 
only which carry the young in pouches after exclusion, similar to what has been observed in 
the family Syngnathide among the fishes. It is also stated to migrate regularly into fresh 
water, but I have had no opportunity of verifying the fact. It occurs on both sides of the 
Atlantic. 
(EXTRA-LIMITAL.) 
Genus Diastyuis, Say. Thorax smooth, six-jointed; the anterior larger than all the others, com- 
pressed and rostrated; the four antenne placed on the same plane. Five pairs of bifid feet ; 
the anterior truncated. Abdomen five-jointed; the first and second with natatory feet. Tail 
with a single bifid style on each side of the first segment. 
Oss. I place this genus where it was supposed by its author to belong. He did not observe 
the eyes, which he says were probably retractile. All the species of this order, hitherto ob- 
served, have pedunculated eyes. It may possibly be the young of some other crustacean. 
D. arenarius. (Say, loc. cit. p. 314.) Thorax minutely crenate on the anterior portion of the sides. 
Lateral caudal styles divaricated, longer than the tail; terminal style less than half the length of 
the lateral ones. Length, 0+2. Pools on the coast of Georgia and Florida. See Monraeo, 
Linnean Transactions, Vol. 7, pl. 6, for C. scorpoides, which Mr. Say thinks a congeneric 
species. 
GENUS SQUILLA. Fabricius. 
Shield divided into three lobes. Lateral appendix of the three last pair of thoracic feet slen- 
der and pointed. External antenne terminating in a broad oval ciliated plate. Second pair 
of jaw-feet expanded into large lamellar hand-claws, stoutly toothed on the edges. 
SQUILLA EMPUSA. 
PLATE XIll. FIG. 54. 
(STATE COLLECTION.) 
Squilla empusa. Say, Jour. Acad. Nat. Sciences, Vol. 1, p. 250. 
S. id. MiLNE-Epwarps, Hist, Nat. des Crustacés, Vol. 2, p. 525, 
Description. Thorax narrowed in front, dilated behind, and deeply concave on the posterior 
margin. Surface with a medial longitudinal ridge, and two on each lateral lobe ; the interior 
short, the exterior terminating abruptly before it reaches the posterior rounded termination: an 
obtuse angle on the side of this lobe, which is not very obvious in the desiccated specimen. 
Anterior margin with slightly prominent spines. Last joint of the hand-claw slender, with 
