110 THE VOYAGE OF H.M.!?. CHALLENGER. 



broken and spinous ; end view irregularly hexagonal, much higher than broad. The 

 middle of each valve bears an irregularly lacinated longitudinal ridge, from which the 

 surface slopes away in an undulating curve to the dorsal and ventral margins, the curved 

 surface being more or less tuberculated or spinous ; within the anterior and ventral margins 

 runs a plaited or dentated ridge ; and the whole circumference bears rows of spines as 

 before described. Length, 1-3 3d of an inch ("77 mm.). 



This species was found only in a dredging from a depth of 2 to 10 fathoms at Port 

 Jackson, Australia. It is either identical with, or very nearly allied to, a form found in 

 the Mediterranean, and previously assigned by me to Cythere subcoronata, Speyer, but 

 which I now think to be distinct from that species. And it is just possible that an 

 Australian species described in the same memoir {Cythei'eis militaris) may represent a 

 very yoimg form of Cythere clavigera. 



[PI. XXIII. fig. 7, a-d. a Shell seen from left side, h from above, c from below, d 

 from front. All magnified 50 diameters.] 



84. Cythere squcdidentata, n. sp. (PL XXIII. fig. 8, a-d). 



Shell tumid behind, compressed in front ; seen from the side much higher in front 

 than behind, the greatest height ecj^ual to two-thirds of the length ; anterior extremity 

 broad and boldly rounded, posterior narrow and truncated ; dorsal margin sloping steeply 

 backwards, and bearing on each valve a series of four long curved slender spines, arranged 

 one behind another, the hindermost being the longest ; ventral margin nearly straight ; 

 seen from above the shell is broadly club-shaped, the greatest width equal to more than 

 half the length, and situated behind the middle ; at this point the sides are very pro- 

 tuberant, running forwards towards the front in a sinuous line, and backwards with a 

 full curve, from the middle of which, on each valve, springs a strong spine pointing 

 obliquely backwards and outwards ; the anterior extremity is truncated, and has a deep 

 central emargination ; the posterior broadly rounded and dentate ; end view irregular, with 

 strongly jagged margins. Surface of the shell very irregularly undulated and finely 

 punctate, length, l-70th of an inch (-38 mm.). 



One specimen only was found in a dredging from Station 323, lat. 35° 39' S., long. 

 50° 47' W., 1900 fathoms. 



[PI. XXIII. fig. 8, a-d. a Shell seen from left side, b from above, c from below, d 

 from front. Magnified 80 diameters.] 



85. Cythere tricristata, n. sp. (PI. XXIII. fig. 6, a-d). 



Seen from the side, the shell is quadrangular, highest near the front, the height 

 at that point lacing equal to more than half the length ; anterior extremity broadly 

 rounded, posterior narrow and truncated ; dorsal margin sloping rather steeply back- 

 wards, ventral nearly straight, the entire circumference broken into broad, blunt tooth- 



