423 



which it may be observed swimming freely during, perhaps, all 

 seasons of the year. The author describes it under the name 

 of Notodelphys ascidicola, and assigns to it the following ge- 

 neric characters : 



Notodelphys,* Mihi. 



Gen. Cha. — 5orfy elongated ; head scutiform, and bearing 

 in front a solitary median eye ; antennae two, filiform, multi- 

 articulate ; mouth with a pair of mandibles, and surrounded 

 by five additional pairs of appendages, of which the anterior, 

 as well as the last two pairs, are prehensile ; thorax having 

 but two rings distinct, the anterior one being confounded with 

 the head. Female with a large dorsal ovigerous receptacle 

 immediately behind the last distinct thoracic ring. Locomo- 

 tive yee^, four pairs; biramous natatory, each pair having an 

 intermediate plate ; abdomen with about five rings, the last of 

 which is terminated by two setigerous appendages. 



Species unica. — iV. ascidicola. Hah. — swimming freely 

 in the branchial sac of Ascidia communis, Irish and English 

 coasts. 



The author, after entering into numerous details relative to 

 the anatomy of the new entomostracon, and describing four 

 distinct phases in its development, maintained that the ovige- 

 rous receptacle was formed by a peculiar development of the 

 dorsal arches of a certain number of posterior thoracic rings, 

 and that it was the true representative of the singular, elytroid, 

 dorsal appendages of the thorax in Anthosoma, Cecrops, and cer- 

 tain other suctorial Crustacea. He was, moreover, of opinion, 

 that the genus Notodelphys presents us with a most interesting 

 transitional form between the true entomostraca and the suc- 

 torial Crustacea. Its perfect mandibulate mouth will at once 

 place it with the former, — a position, indeed, which its highly 

 developed natatory feet and active habits, as well as its general 



From I'uJroe, tergum, and ci\(pvg, matrix. 



