REPORT ON THE LAMELLIBRANCHIATA. 157 



curvotl, ami decideclly more descending. Tlierc is in the left valve a single oblique lamellar 

 tooth which is situated behind the umbo forming the posterior boundary to a narrow deep 

 groove which is as it wore lobed in front and extends a little beyond the apex of the beak. 

 The muscular scars and pallia! impression are very indistinct. 



Length 4i mm., height 4, diameter 3. 



i/a^iirt^.— Station 244, Mid North Pacific Ocean, at a depth of 2900 fathoms; red clay. 



A single specimen from the above great depth (nearly three and a third miles) was 

 dredged up perfect, both as regards the shell and animal. In endeavouring to open the 

 valves in order to determine the genus some slight damage was done, and it became 

 necessary to boil the specimen so that the adductor muscles should relinquish their hold 

 and allow the valves to separate. Unfortunately, the hinge-plate of the right valve was 

 destroyed, but, judging from the left valve, its construction must have been all but 

 identical with that obtaining in the following species. 



CaUocardia (?) atlantica, n. sp. (PI. VI. figs. 8-8?>). 



Testa CallocardicB pacificce similis, sed brevior, seque longa ac alta. 



Beyond the difference in form there is very little to distinguish this species from 

 CaUocardia pacijica. It is a very remarkable fact that shells so similar should exist at 

 such great depths, at such remote localities, which, however, are situated almost upon 

 the same parallels. 



On placing side by side specimens of KeUiella miliaris from Hardanger Fiord, 

 Norway, kindly furnished me by the Rev. A. M. Norman, with the Challenger examples 

 of this species, and others from Davis Strait obtained by the " Valorous " expedition, 

 and regarded by Dr. Gwyn Jefireys as the fry of Isocardia cor, I observe certain 

 distinctions. In the first place, I have never seen or heard of a KdUellct from Norway 

 attaining to the size (4 mm.) of the specimen from Station 73. In the next place, I 

 perceive a difference in form, the ventral outline of these specimens being decidedly 

 bulged or more excurved than that of KeUiella. In addition to this, there is a slight 

 variation in the dentition, which accurate figures alone could well explain, and finally, 

 in the minute specimens in question, I find a slight dorsal ridge, which marks off a 

 posterior area, of which ridge I can discover no trace in KeUiella. 



The fry of CaUocardia adarnsii must resemble this species very closely in form 

 and dentition, but, judging from the apices of the known specimens, which may not, 

 however, be full grown, it would be more strongly concentrically sculptured. 



Length and heio-ht 4 mm. 



Habitat. — Station 73, west of Azores, in 1000 fathoms; also Station 78, off San 

 Miguel, at a depth of 1000 fathoms. 



