ACADEMY OF SCIENCES. 



117 



esting species were not received, that I could have furnished the Academy a 

 good series. 



Idotcea marmorata, n. sp. 



Body rather elender; outer antenna about half the length of the body; fifth 

 joint nearly equal to the united length of the third and fourth. The pos- 

 terior margin of the cephalon and the anterior margin of second segment, 

 dorsdly contiguous. Four first segments of the pereion equal, and about one- 

 third longer than either of the followiug. The emarginated caudal shield is 

 longer than the four preceding segments. 



Length, H- 



I place the above species in the genus Idotcea, in which Milne Edwards 

 includes Steuosomce and Sidur ce, of Leach, and the Leptosomce, Hebe, Oliskce, 

 Zenobice, and Armidce, of Risso. Our specimen possesses the loug antenna 

 and somewhat slender form of Steuosomce. The suture between the first and 

 second segments of the pleon is just discernible at the lateral outline only, 

 no trace of it being visible when viewing the caudal plate from above. Our 

 specimen was collected and sent to us by Mr. W. J. Fisher, from the west 

 coast of Lower California. It is a very pretty species, its marbled coloration 

 suggesting the specific name we have given it. 



Idotcea muricata, n. sp. 



Outline elliptical. First four segments of the pereion equal, the last three 

 decreasing gradually; each segment traversed by a transverse dorsal ridge, 

 bearing three muricoid spines, between which and the lateral margin of each 

 segment are from four to six small tubercles. Abdomen rapidly narrowed 

 to an obtuse, horn-like point. Eyes prominent. Antenna not seen. 



Length, fg i Q - 



The specie-! above described was obtained by Mr. W. J. Fisher, from Icy 

 Cape, about three y. ars ago. Its very rough dorsal surface clearly distin- 

 guishes it from all other members of the genus with which we are acquainted; 

 in fact, it differs so greatly from all species of Idotcea we have hitherto seen, 

 that we were inclined to form a new genus for its reception; but as no less 

 than seven genera are included in Idotcea by M. Edwards (and subsequently 

 by Bate and Westwood) , of some of which we have not seen the descrip- 

 tions, we have placed it as above. Our single specimen is without antenna, 

 they having been broken off in transit. 



The eyes are prominent, and in advance and above each is an irregular 

 shaped and apparently hollow spine, posterior to the frontal outline of the 

 head, at a distance equal to their heighth. The cephalon, like the body, pos- 

 sesses the same rough tuberculose character. 



The Secretary read the introduction of a paper " On the De- 

 termination of the Constant g,' communicated through the Cor- 

 responding Secretary by E. Dyer. 



