CYTHERE. 169 



obtuse. The shell of the male is longer, narrower, and distinctly quadrangular, and its 

 infero-posteal angle is produced into a more or less conspicuous squamous and spinous 

 plate. The surface of the shell is marked by large subhexagonal excavations, the intervals 

 between which are beset with several strong spines of irregular shape and size, which are 

 much larger in the male than in the female ; there is also a row of spinous tubercles 

 parallel to and a little within the anterior margin, the series being continued with 

 less regularity along the greater part of the ventral margin. Hinge-tubercles large, 

 shining, and prominent, especially in the male. Hinge-teeth very strongly developed, 

 shell very thich and strong. 



Length, -^th of an inch. 



Cytlere Bunelmensis is not very rare in the living state in the seas of Norway, 

 Scotland, and Northern England, mostly inhabiting depths of fifteen fathoms and 

 upwards. The reticulation of the surface is often obscure, and its spinous armature is 

 very variable in strength and general development. Young specimens (fig. 19) are sub- 

 ovate in form, with the margins arched and the angles well rounded off. The form 

 figured in Plate XI, figs. 36, 37, which we at one time supposed to belong to a distinct 

 species, is without doubt the young stage of C. Dunehnensis ; between this and the adult 

 form almost all gradations of growth have been observed. 



Distribution. Becent. — Great Britain and Ireland, Gulf of St. Lawrence, Arctic Seas, 

 Spitzbergen. 



Fossil. — England : Bridlington. Scotland : nearly all the Post-tertiary beds. Ireland : 

 Belfast and Woodburn. 



38. Cythere Whiteii {Baird), Plate XII, figs. 1—3. 



1850. Cythebeis Whiteii, Baird. Brit. Entom., p. 175, pi. xx, figs. 3, 3 a. 

 1868. Cythere — Brady. Monog. Rec. Brit. Ostrac, p. 416, pi. xxx, 



figs. 21—24. 



Carapace, as seen from the side, oblong, quadrangular, nearly equal in height 

 throughout, height equal to half the length ; anterior margin rounded and more or less 

 spinous, conspicuously elevated over the anterior hinge-joint ; posterior almost rectangu- 

 larly truncate, and mostly bearing two or more large backward-pointing spines at its 

 lower termination ; superior and inferior margins almost straight, but more or less 

 bluntly toothed behind the middle. Seen from above, the outline is ovate, widest behind 

 the middle, the greatest width being somewhat less than the height, only slightly tapering 

 towards the broadly mucronate or sub truncate extremities. The valves are ornamented 



22 



