178 THE VOYAGE OF H.M.S. CHALLENGER. 



the male carapace (fig. 2, a-d) are much more slender than those of the female. Length, 

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



The type specimens described in Les Fonds de la Mer were dredged at Hong Kong ; 

 those described in the present monograph are from lat. 9° 49' S., long. 137° 50' E., 28 

 fathoms, mud (Station 189); and from Hong Kong Harbour, 7 fathoms, mud; Port 

 Jackson, 2 to 1 fathoms ; off Booby Island, 6 to 8 fathoms. 



[PL XLHI. fig. 1, a-g. a Carapace of female seen from left side, b from above, c from 

 below, d from front ; e young shell seen from left side, / from above, g from front ; fig. 

 2, a-d, a shell of male seen from left side, b from above, c from below, d from front. 

 All magnified GO diameters.] 



12. Cytherella irregidaris, n. sp. (PL XLIH. fig. 3, a-c). 



Valves as seen from the side subquadrangular, scarcely higher in front than behind, 

 height equal to nearly two-thirds of the length, anterior extremity well rounded, posterior 

 flattened, obliquely truncate, dorsal margin slightly excavated, ventral somewhat convex 

 along its whole course.; seen from above the lateral margins are nearly straight, ending 

 in an obtusely angular fashion before and behind and thence tapering abruptly to the 

 extremities. The shell-surface is undulated, having a large irregular elevated central 

 patch which is fiUed with small oblong puncta arranged in obscurely concentric series. 

 Length, l-50th of an inch ("5 mm.). 



One or two detached valves of this species were noticed in a dredging from 435 

 fathoms off Bermudas (Station 33). 



[PL XLin. fig. 3, a-c. a Left valve seen from outside, b from above, c from front. 

 All magnified 60 diameters.] 



13. Cytherella latimarginata, n. sp. (PL XXVL fig. 7, a-d). 



Carapace compressed, oblong ; seen from the side, subovate, scarcely higher in front 

 than behind, height equal to about half the length ; extremities well rounded, dorsal 

 margin slightly convex, ventral somewhat sinuated in the middle ; seen from above, the 

 outline is subcuneiform, but only very little broader behind than in front, the greatest 

 width being equal to fully one-third of the length ; the lateral margins are subparaUel, 

 with a long central protuberance, terminating al^ruptly at each extremity, and thence 

 converging at an obtuse angle towards the median line of the shell ; end-view irregularly 

 ovate. The surface of the shell is irregularly undulated, the margins raised into a broad 

 rounded lip, which forms an encircling fillet, except at the anterior margin, where it is 

 partially absent. Length, l-50th of an inch ('5 mm.). 



Two or three specimens only of this species were found in a dredging from Torres' 

 Strait, 155 fathoms, sandy bottom. The shells figured in the plate represent, probably, — 

 judging from the difference of size,- — different stages of growth, the essential characters of 



