INTRODUCTION— CONCHCECIADtE, ETC. 5 



2. Conchceciada, — "Shell very thin and flexible, neither horny nor calcareous, but 

 almost membranaceous, more or less distinctly notched and emarginate in 

 front, forming an orifice, through which, as in the preceding family, the lower 

 antennae are protruded whilst swimming " (Brady, op. cit., p. 468). 



1. CoNCHCECiA, Dana. 



" Valves elongated [subrectangular in outline], produced in front into a beaked 

 process ; shell finely reticulated, or marked with concentric striae ; very sUghtly pilose. 

 Dorsal surface of the carapace flattened in front, sometimes slightly excavated and keeled " 

 (Brady, op. cit., p. 469). 



2, Halocypris, Dana. 



Valves thin, subquadrate, saddle-shaped ; more or less beaked in front at the upper 

 angle. 



3. Eniomoconchidce} 

 Carapace strong and large, gibbous, subquadrate or suborbicular in side-view. 



1. Entomoconchus, M'Coy. [Known only in the fossil state.] 



Carapace subglobose, hinged by overlap ; notched in front with a slight beak, and 

 long, vertical, interrupted gape. 



2. Heterodesmus, G. S. Brady. 



" Carapace subglobose. Dorsal margin slightly arched, forming at its extremities 

 two largely developed hinge-processes ; the anterior process somewhat waved and scroll- 

 like ; the posterior a truncate cone, projecting directly upwards. Ventral margin strongly 

 arched " (Brady, 'Trans. Zool. Soc.,' vol. v, p. 387). Mr. Brady regards Heterodesmus 

 as closely related to the Ci/pridinadcB, though not yet wholly elucidated ; and he has 

 suggested the alliance with Entomoconchus as above. 



' G. S. Brady, 'Trans. Linn. Soc.,' vol. xxvi, 1868, p. 358. 



