104 



THE VOYAGE OF H.M.S. CHALLENGER. 



73. Cythere tetrica, n. sp. (PI. XXIII. fig. 5, a-d). 



Carapace, seen from tlie side, oblong, subovate, greatest height near the front, and 

 equal to half the length ; anterior extremity rounded and divided into numerous small 

 crenulations ; posterior subtruncated, sKghtly jagged, rounded off at the angles ; dorsal 

 margin sloj)ing gently from the front and broken up by numerous irregular indentations ; 

 ventral nearly straight ; seen from above, the outline is ovate, more than twice as long- 

 as broad, with gently curved subparallel sides, and broadly rounded extremities, the 

 margins throughout very much broken; end view irregularly ovate, with a lateral 

 tuberosity on each side above the middle. The surface of the shell is thickly covered 

 with large nodules of irregular size and shape, and has an irregular longitudinal ridge 

 just within the ventral margin. Length, l-45th of an inch ("53 min.). 



Dredged off Booby Island, lat. 10° 36' S., long. 141° 55' E., 6 to 8 fathoms 

 (Station 187). 



[PI. XXIII. fig. 5, a-d. a Shell seen from left side, h from above, c from below, d from 

 front. Magnified 60 diameters.] 



74. Cythere acanthoderma, n. sp. (PI. XVIII. fig. 5, a-e). 



Shell oblong, subovate, tumid, covered everywhere with more or less strongly-developed, 

 very irregular, blunt and ragged spines ; seen from the side, the valves are subovate or 

 somewhat pear-shaped, highest near the front, the height being equal to nearly two-thirds 

 of the length ; anterior extremity well rounded, posterior produced in the middle ; dorsal 

 margin sloping backwards and very much laciniated, ventral slightly convex ; seen from 

 above, the outline is subovate, not twice as long as broad, widest near the middle ; sides 

 curved, converging gradually towards the front and abruptly behind ; extremities wide and 

 truncated ; the end view is subtriangular, equilateral, with convex sides and rounded 

 angles ; the margins of the shell, from whatever aspect it is viewed, are excessively 

 rugged, and the spines with which it is everywhere thickly beset have a tendency to 

 enlarge at their apices, often becoming bifurcate or even trifurcate ; in this character it 

 differs very remarkably from the next species {Cythere dasyderma), in which the spines 

 never take on any development of this nature. Cythere acanthoderma occurred in 

 moderate numbers in several of the Challeno-er dreda;inos : — 



Lat. 35° 35' K, long. 50° 27' W., 



I 



I 



Like Cythere dictyon and Cythere dasyderma this species seems to be cosmopolitan in 



