STATE GEOLOGIST. 85 



head is much as in the last, but it is not certain that the beak is 

 cleft, although it has a peculiar form (not indicated in the figure) 

 near the end. The length is 0,7 ram. The terminal setse of the 

 antennules are very unequal; but in most points, as in the armature 

 of the post-abdomen, the details resemble C. macrurus. 



III. — Genus Alonopsis, Sars. 



This curious genus includes three species of small lynceids, 

 which exhibit a combination of characters The form of the beak 

 and head is like that of Pleuroxus, which the form and sculpture of 

 the shell otherwise resembles. The back is extended more or less 

 in a knife-like ridge above, thus resembling Acroperus, a resemblance 

 hightened by the excavated lower margin. The form of the post- 

 abdomen approaches that of Acroperus, but in that genus it is of 

 about equal width throughout and in this it rapidly narrows. The 

 internal organs and feet are of the typical lynceid form, while the 

 antennae are as in Pleuroxus. 



The type of the genus, A. elongata, is apparently much closer to 

 Acroperus than the two species which have been identified in 

 America. 



Shell sub-rectangular, high, produced into a ridge above; lower 

 margin convex anteriorly, concave behind; beak rather long; an- 

 tennules slender; antennae with eight seta3; abdomen long, nar- 

 rowed toward end, incised at the extremity; claw rather large, with 

 median spines and a basal thorn; third foot with a long bristle. 

 Male smaller, without the carina above; orifice of sexual organs in 

 front of the claw, which is removed from the anterior margin. The 

 young are more elongate and (sometimes) have hexagonal reticula- 

 tions instead of the usual strong diagonal strife. Motion slow. 



Sp. 1. Alonopsis elongata, Sars. 



Lynceus macrurtis, LIHVIN. 



Lynceus mnxirurus, ZENKER, LEYDIG. 



Alorui elongcUa, SARS. 



Acroperus inierviediiis, SCHOEDLEB. 



Alonopsis elongata, P. E. MUELLER. 



The shell is wide, the upper margin forming an even curves 

 manifestly angled behind; ventral margin nearly straight, ciliated 

 throughout, with a single tooth behind. Fornices large; head nar- 

 row, not carinate. Post-abdomen compressed, truncate at the end, 

 armed with a series of marginal spines and of lateral scales; caudal 

 claws large, with a single spine at the base and two median spines 

 followed by a series of minute seta3. 



