OF THE ANTWERP CRAG, 391 
greatest width in the middle and fully equal to half the length. End view subtri- 
angular with convex sides, nearly equilateral. Surface of the shell slightly undulated, 
devoid of sculpture, except that a thin curved aleform ridge is developed towards the 
ventral margin of each valve; the anterior margin bears below the middle a variable 
number of short, blunt, irregular spines: and there are usually two or three of similar 
character at the posterior extremity of the shell; the lateral ala often has a single spine 
a little behind the middle; and the ventral surface of the shell is more or less marked 
with flexuous longitudinal grooves. Length 3'5 inch (1:3 millim.). 
Cythere tarentina has not previously been observed in the fossil condition ; but it still 
lives in many parts of the Mediterranean. It is a very distinct and fine species. Several 
specimens have been found in the sand from the Panopea- and Pectunculus-beds. 
CyTHERE acuticosta, Egger. (Plate LXVI. figs. 5 a—6 d.) 
Cythere acuticosta, Egger, op. cit. p. 40, pl. vi. fig. 7. 
Carapace, as seen from the side, rhomboidal, equal in height throughout; height 
equal to nearly two thirds of the length ; anterior margin obliquely rounded off ; posterior 
obliquely truncate below the middle, rounded off above ; dorsal margin straight ; ventral 
also straight, except the anterior half, which is a little upturned, Seen from above, the 
outline is elongated, subhexagonal or subovate, sides nearly parallel but irregularly 
flexuous, width equal to half the length, tapering rather abruptly towards the extre- 
mities, which are pointed. End view quadrangular with irregularly waved sides, width 
equal to three fourths of the height. The surface of the shell is strongly sculptured 
with sharply cut ridges, running for the most part in a longitudinal direction, but 
irregularly flexed and anastomotic; one of them, more developed than the rest, is in 
the median line; the furrows between these ridges are excavated into pits of very 
irregular size and shape; the dorsal surface is marked by a very distinct longitudinal 
median groove with raised ridges; and the ventral surface has on each valve a flattened 
aleform plate which is sculptured with transverse and marginal excavations. Length 
as inch (0°54 millim.). 
Our specimens of this species occurred in the Pectunculus- and Panopwa-beds. 
Though the figures given by Dr. Egger differ rather considerably (especially in the end 
view) from my own, I am disposed to think that they are meant to refer to the same 
species, and on that supposition have adopted the specific name acuticosta. 
CYTHERE TRAPEZIA, nov. sp. (Plate LXVI. figs. 4 a4 d.) 
? Cythere corrugata, Egger, op. cit. p. 35, pl. v. fig. 3. 
Carapace, as seen laterally, trapezoidal, rather higher in front than behind, height 
equal to more than half the length; anterior extremity obliquely rounded ; posterior 
subtruncate, rounded a little below, the lower angle not produced ; dorsal and ventral 
margins nearly straight, the latter very gently situated in the middle. The outline from 
