Family Asteropidae. 



Fam. Asteropitlae, U. S. Bkadv aiul A. M. Xoii.M.w, 1896, p. 628. 

 Sub-Fiim. Cylindroleherinae, G. W. MCller, 1906 b, p. 32. 

 Asteropinae, G. W. MOlleh, 1912, p. 42. 



Description: — Shell: — This shows sexual dimorphism. — It has a well-developed 

 rostrum. The iucisur is rather deep; in most cases, the inner (posterior) part of the upper incisur 

 lip covers the inner part of the lower incisur lip, with which it is also united at its innermost 

 part. (This is expressed by G. 0. Sars, 1887, p. 186 as follows: The rostral incisur ,,er nedentil 

 begraendset af en indad skraat fremspringende, staerkt chitiniseret Lamelle".) The selvage 

 varies in type, sometimes being rather broad, with a smooth margin, sometimes almost quite 

 absent or divided into fine, short hairs. The list runs in an even closed bow from the rostral 

 incisur along the ventral and posterior margins of the shell, coming to an end posteriorly near 

 the hinge of the shell; it is in most cases narrow along the ventral margin of the shell, and some- 

 what wider inside the posterior margin of the shell. The distance from the list to the margin 

 of the shell is on the average somewhat greater along the posterior margin of the shell than along 

 the ventral margin. The valves are always joined along less than half the circumference. Con- 

 trary to the females, the males are always characterized by a ring of long hairs round the posterior 

 part of the shell; in some forms, however, this wreath of hair is very sparse. 



First antenna: — This shows rather strong sexual dimorphism. — The sensory 

 bristle of the fifth joint is always developed. The original sixth joint has always only one bristle, 

 situated distally-medially. This antenna has six or seven bristles distally, three of which are 

 probably to be considered as belonging to the original seventh joint, and from three to four 

 probably belong to the original eighth joint. In most cases, perhaps always, the anterior 

 end bristle is claw-shaped. 



Second antenna: — This shows dimorphism. — The endopodite in the 

 female is small and weak, in the male it is always developed as a three- jointed clasping organ; 

 the end joint of this branch has only one bristle, fixed distally in the females, proximo-ventrally 

 in the males. 



Mandible: — This has rather slight sexual dimorphism (sometimes even none at 

 all?). — The protopodite joints, like the two proximal endopodite joints, are 



