OUCUKSTIDJ?. 35 



This genus has been establislied by Dana to receive those Amplii- 

 poda which strongly assimilate to the Orchestiir, but have the supe- 

 rior antennae of greater length and importance. In the Orcli€sti(t 

 they are almost nidimcntary ; in this genus they reach quite to, and 

 often beyond, the pedimcle of the inferior. 



The peduncle of the inferior antennae has only three joints ex- 

 posed; but the first two are not so completely fused with the 

 anterior (or facial) wall of the head as in Orchestia and TaUtrns. 

 A small olfactor)- denticle is visible. The mandibles are without 

 appendages. The maxillipeds terminate in a shai-p unguiculate 

 dactylos. The propoda of both pairs of gnathopoda are subchcliform 

 in both sexes ; the anterior pair small, the second generally larger 

 and more powerful. In the female, those of the second pair, although 

 occasionally smaller than in the male, are never rudimentaiy, and 

 have the carpus produced more or less along the inferior margin of 

 the propodos. 



The coxae are squamiform and well developed, scarcely so deep as 

 the body of the animal ; those of the third pair of pereiopoda are 

 shorter than the fourth and subequally chvided, the posteiior half 

 being generally the smaller. The pereiopoda are short and robust ; 

 the thii'd paii- are generally the shortest. 



The two penultimate pairs of pleopoda arc short and strong, with 

 double short styliform rami ; the posterior pair are furnished with 

 but a single branch. The telson single. 



In habit, as in structure, AUorcliestes occupies a position between 

 Orchestia and the Gammariform type. It is a true littoral genus, 

 dwelling under weed fresh wetted by the sea, in shallow pools and 

 crevices of the rocks which the tide leaves bare at every ebb. Only 

 one species, so far as we are aware, has been taken with the di'edge : 

 A. media was so taken in two or three separate localities. 



The length of the upper antennoe, the presence of an olfoctoiy 

 denticle upon the inferior antennae, and the small size of the coxae 

 of the third pair of pereiopoda are ex-idcnces of an approximation 

 towards the IVATAToniAL tribe ; whereas the incoi-poration of the 

 basal joints of the inferior antenna? in the anterior wall of the 

 cephalon, the absence of any appendage to the mandibles, the large 

 size of the second pair of gnathopoda, the shortness of the posterior 

 pleopoda, which are also single-bx'anchcd, the robust character of 

 the pleon, and the sti'ucture of the demial tissue, together with the 

 short stiff hairs, are all marks that draw the animal near to that of 

 Orchestia. 



Under the name of Ennne (Eur. Merid. p. 96), Eisso has described 

 a genu-s that appeare to be identical with this ; but his description is 

 not sufficiently distinct to allow of that name being used even as a 

 synonj-m. 



1. Allorchestes Piedmontensis, n. s. (Plate I. a. fig. 5.) P.M. 



Eyes small and round. The upper antennae not longer than the 



pedimcle of the lower. Lower antennae about half the length of 



d2 



