142 THE VOTAGE OF H.M.S. CHALLENGER. 



perhaps referable to a variety of this species, were dredged in Torres' Straits, and are 

 figured in Plate XXXII. fig. 2, a-c ; their chief characteristic being a large tubercle on 

 the dorsal portion of the valve. 



[PI. VI. fig. 6, a-d. a Eight valve seen from side, b from above, c from below, d 

 from front ; magnified 60 diameters. PI. XXXII. fig. 2, a-c. a Right valve seen from 

 side, b from above, c from front ; magnified 50 diameters.] 



2. Bythocythere arenacea, n. sp. (PI. XXXIII. fig. 3, a-g). 



Carapace of the female, seen from the side, oblong, somewhat helmet-shaped, trun- 

 cated in front, acutely pointed behind, height equal to about half the length ; anterior 

 extremity nearly straight, looking obliquely upwards, rounded ofi" at the upper and 

 lower angles, posterior extremity much produced, and ending in an acute median point ; 

 dorsal and ventral margins straight, and almost parallel ; seen from above the lateral 

 margins are strongly convex, converging with a gradual curve towards the front, and 

 almost at a right angle behind the middle, then running backwards to form a broad, 

 triangular, acutely pointed posterior projection ; end-view quadrangular, broadest at the 

 base, ventral line strongly convex, dorsal about one-third as long, and deeply concave, 

 lateral margins moderately convex. The surface of the shell is covered with small 

 tubercular elevations of a coarsely granular or arenaceous appearance ; the lateral alae are 

 only moderately prominent, and end behind in a rounded angle. The shell of the male 

 differs from that of the female chiefly in being more elongated and less tumid. Length, 

 l-37th of an inch (7 mm.). 



The characters of Bythocythere arenacea, both as to shape and surface markings, 

 sufiice to distinguish it very obviously from any other s|)ecies. Several examples occurred 

 in a dredging from Torres' Straits, lat. 11° 35' S., long. 144° 3' E., 155 fathoms 

 (Station 185). 



[PL XXXIII. fig. 3, a-g. a Carapace of female seen from left side, b from above, c 

 from below, d from front ; e male right valve seen laterally, f from below, g from front. 

 All magnified 50 diameters.] 



3. Bythocythere pumilio, n. sp. (PL XXXIII. fig. 4, a-d). 



Carapace elongated, tumid, depressed ; seen from the side, oblong, quadrangular, nearly 

 equal in height throughout ; height equal to less than half the length, anterior extremity 

 subtruncate, scarcely rounded, posterior rather narrower, imperfectly rounded, obscurely 

 dentated below the middle; dorsal margin nearly straight through its whole length, ventral 

 slightly convex, dentate in front, ending behind in an alseform projection, which is mucro- 

 nate at the angle ; seen from above the contour is hexagonal, with parallel sides, the width 

 equal to somewhat less than two-thirds of the length ; sides converging equally and rather 

 abruptly, and ending in a subacuminate process both in front and behind ; the posterior 



