REPORT ON THE LAMELLIBRANCHIATA. 2V) 



On comparing the type of Thecalia macrotheca presented to tlie British Museum b)^ 

 G. F. Angas, Esq., with South African specimens of this well-known form, I cannot detect 

 the slightest difference. With the above type Mr. Angas also gave four specimens with- 

 out any internal cup-like process, which may be the male, if the sexes really be separate, 

 as stated by Messrs. H. and A. Adams, of Cardita concamerata. Adams and Angas 

 mention that this cup-shaped appendage is much larger in their species than in the Cape 

 shell. As the size of this is found to vary when a good series of specimens is examined, 

 this difference, which I do not observe, however, in the type, seems to me of little 

 importance. On opening one of the Challenger specimens the cup was found to contain a 

 number of fry. The foot is small, cleft at the bottom, and furnished with a byssus. 



Two specimens which have no sinuation at the ventral margin, and lack the internal 

 cup, are probably males. They are rather squarer at the anterior end, and the ridges down 

 the hinder part are finer and one or two more in number. 



Carditella, Smith. 



Carditella exidata, n. sp. (PL XV. figs. 6-6«). 



Testa transversa, subquadrata, crassiuscula, valde inEequilateralis, albida, mediocriter 

 convexa. costis radiantibus circa quatuordecim rotundatis, concinne squamulatis instructa. 

 Latus anticum fere perpendiculariter truncatum, posticum latins, rotundatum. Margo 

 dorsi horizontalis, rectus, ventralis late arcuatus. Umbones parvi, acuti, fere terminales. 

 Pagina interna nitida, alba, radiatim sulcata. 



This minute species, externally, is very much like the young of Cardita calyculata, 

 but more finely squamulated, and without the slight sinuation in the ventral margin 

 occurring in that species. It is whitish, very inequilateral, squarish-oblong, obliquely or 

 almost perpendicularly truncate in front, rather broad and rounded behind. The dorsal 

 margin is about horizontal and rectilinear, and the ventral very gently arcuate. The 

 beaks are small, acute, and all but terminal. The sculpture consists of about fourteen 

 radiating rounded ribs, of which those on the hinder half of the valves are considerably 

 broader than the rest, and separated by broader and deeper grooves, which do not, how- 

 ever, equal in width half that of the ribs, which are finely and closely scaled throughout. 

 The interior of the valves is glossy, white, and radiately^ grooved, the grooves correspond- 

 ing to the external costal. The hinge consists of a single central conical triangular tooth 

 in the right valve, which fits in between two more slender divergent teeth in the left. 

 The lateral teeth are well developed and equidistant. 



Length 4 mm., height 2f, diameter 2. 



Habitat. — Station 135, off" Nightingale Island, Tristan da Cunha, in 100 to loOfathoms. 



This pretty little species is more oblong and inequilateral than any of the other 

 forms belonging to this genus, all of which are shells of very small size. 



