On Steno cypris Chevreuxi. 



being verv delicate and densely crowded, whereas those of 

 the posterior extremity appear much coarser and more 

 distant, some being of very considerable length. In the 

 centre of each valve, somewhat in front of the middle, the 

 insertion for the adductor muscle of the shell is easily observ- 

 able as a number of well-defined clear spots, the 2 anterior 

 of which lie somewhat apart from the other 4 (see figs. 1,4). 

 The valves are very unequal in size, the left one (see 

 fig. 3) being much larger than the right (fig. 4), and over- 

 lapping it considerably both in front and behind, as also 

 along the ventral face (see fig. 1). The form of the two 

 valves also appear, when isolated (comp. figs. 3 and 4), 

 rather dissimilar, the left one (fig. 3) having the anterior 

 extremity rather more deflexed, and the posterior one some- 

 what broader than the right valve (fig. 4). The inner 

 duplicatures are rather large, especially that of the anterior 

 extremity. On the left valve (fig. 3) this anterior dnplicature 

 exhibits the usual semilunar, shelf-like form, and has a 

 transversely striated peripheric area surmounted by a pellucid 

 rim. On the right valve (fig. 4), this duplicature has a 

 rather different appearance, forming inside a rounded ex- 

 pansion, and entirely without any transverse striation. The 

 posterior duplicature is comparatively broader on the left 

 valve (fig. 3) than on the right, and has the peripheric 

 area striated in a similar manner to that of the anterior 

 duplicature: the striation may also be traced along the 

 whole ventral face of the valve. Just within the inferior 

 sinus, both valves form a short lingular expansion extended 

 straight inwards, that of the right valve being overlapped 

 by that of the left, when the shell is closed. As in other 

 Cypridids, the valves are connected along the dorsal face 



2 - Archiv for Math, og Naturv. B. XVIir. No. 7. 

 Trykt den Sde Oktober 1896. 



