REPORT ON THE OSTR4CODA. Ill 



like processes of no great leugtli, but fewer and more prominent on the dorsal margin ; 

 the posterior dorsal angle has one spine somewhat larger and more conspicuous than the 

 rest ; seen from above, the outline is very irregular, consisting of a central mass which 

 has on each side a deep median indentation, and of two broad truncated terminal 

 portions ; seen endwise, it is likewise of irregular form, having two strongly-developed 

 lateral protuberances projecting from a "liroad central portion. The central mass of 

 the shell is bounded on all sides, except the dorsal, by a transversely corrugated en- 

 circling zone, the edges of which are irregularly dentated ; and on the sides of the valves, 

 placed one behind another, in the middle line are three short strongly-elevated crests, 

 each of which is divided into three or four tooth-like segments. Length, l-40th of an 

 inch ("65 mm.). 



Dredged at Port Jackson, 2 to 10 fathoms, and in 16 to 25 fathoms off the Admiralty 

 Islands. 



[PI. XXIII. fig. 6, a-cl. a Shell seen from left side, h from above, c from below, d 

 from front. All magnified 50 diameters.] 



86. Cythere velivola, n. sp. (PI. XXIII. fig. 4, a-c). 



Valves, seen laterally, oblong, much higher in front than behind, height equal to two- 

 thirds of the length ; anterior extremity broadly rounded, divided into numerous broad, 

 blunt squamous teeth of various sizes ; posterior extremely narrow, rounded, and bearing 

 four or five thick, gnarled teeth, those at the ventral angle being longer than the rest ; 

 dorsal margin cut up into several broad squamous j^rocesses, and bearing at its posterior 

 angle a very long and stout curved spine ; the ventral margin is nearly straight, and in 

 the middle third of its course is produced laterally, forming a very strongly projecting 

 alseform plate ; seen from above, the outline is excessively compressed and almost linear, 

 except in the middle, where the lateral ala forms a remarkable angular projection. The 

 general surface of the valves is much depressed and sinks towards the extremities, forming 

 a sort of trough, which is bounded externally by a somewhat elevated and irregularly 

 lacinated belt ; the central area is slightly undulated, and bears a few scattered circular 

 papillae. Length, l-40th of an inch ("65 mm.). 



A few detached valves of this remarkable little species were found in a dredging from 

 Station 189, lat. 9° 59' S., long. 137° 50' E., 28 fathoms. 



[PL XXIII, fig. 4, o-c. a Left valve seen from side, h right valve seen from side, c 

 left valve seen from below. Magnified 60 diameters.] 



Cytheridea, Bosquet. 

 Cijiheridea, Bosquet, Entom. fossil, des Terres tertiair. (1850). 

 Valves unequal, the left mostly larger than the right, ovate or subtriangular, highest 

 in front ; surface smooth, or marked with scattered circular tubercles, impressed puncta 



