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



equal to less than half the length ; the end view forms an irregular pentagon. Surface 

 of the valves coarsely excavated with large, closely-set and irregular fossae, and haviug 

 three conspicuous curved ribs, the largest of which runs lengthwise nearly in the middle 

 of the valve, another rather shorter and near the ventral margin, and a third close to 

 the dorsal margin ; these, in the full-grown shell, all end abruptly behind in angular 

 prominences, and are lost in front on the surface of the shell ; the ribbing and spinous 

 armature are much more fully developed in the male (fig. e). Length, l-33d of an inch 

 (77 mm.). 



This is a characteristic Mediterranean species, and the only specimens brought home 

 by the Challenger, so far as I have seen, are from anchor-mud, brought up from a depth 

 of 11 fathoms in Vigo Bay. 



[PL XXI. fig. 6, a-h. a Carapace of female seen from left side, h from above, c from 

 below, d from front, e male seen from left side ; /, g, h show young forms of the shell. All 

 magnified 45 diameters.] 



42. Cythere quadriaculeata, n. sp. (PL XXIL fig. 2, a-d, and PL XXV. fig. 4, a-d). 



Shell, seen from the side, irregularly quadrate, much higher in front than behind, 

 the greatest height equal to two-thirds of the length ; anterior extremity well rounded, 

 oblique, posterior narrowed, truncated, and emarginate, dorsal margin sloping steeply 

 from the front, and suddenly excavated just in front of the angulated posterior 

 extremity ; ventral margin nearly straight, but up-curved behind the middle ; seen from 

 above, the outline is oblong, subhastate, fully twice as long as broad, widest behind 

 the middle, the sides slightly converging forwards from two spinous projections near 

 the posterior extremity ; behind these projections they converge more abruptly to the 

 middle line ; the posterior extremity is subacute, the anterior more obtuse ; end view 

 angular, five or six sided, lateral margins parallel, ending above and beloAV in sharp 

 projecting processes. Surface of the shell marked with closely-set subrotund excava- 

 tions, and having on each lateral aspect two strongly-marked longitudinal ridges, each 

 of which terminates much behind the middle of' the valve in a sharp spine. Length, 

 l-50th of an inch ('5 mm.). 



Dredged in the Inland Sea, Japan, 15 fathoms (Station 2336), and off the reefs at 

 Honolulu in 40 fathoms. 



This is in general character very like Cythere loolytrema, but it is not so coarsely 

 sculptured, and is devoid of the marginal spines belonging to that species. The ribs in 

 Cythere 2}olytrema are straighter, longer, and more strongly developed, but do not end 

 posteriorly in the conspicuous spines which are characteristic of Cythere quadriacideata. 

 The dorsal and ventral aspects are very different in the two species. 



[PL XXIL fig. 2, a-d. a Shell (Honolulu) seen from left side, b from above, c from 

 below, d from front. Magnified 80 diameters. PL XXV. fig. 4, a-d. a Shell (Japan) 



