MOLLUSKS. 47 



sively to the inner side of the hinge-margin, but partly visible from the 

 outside between the edges of the valves. 



Length of largest specimen, 4"""; height, 3"""; diameter, 2.5""". • 



This minute shell was found attached to the byssus of Mytilus canali- 

 culus, and, at first sight might be readily taken for the fry of that species. 

 An examination of the hinge and muscular scars, however, is sufficient 

 ' to dispel this impression. 



It diflers from Modiolarca, in its single anterior muscular scar, the 

 l)resence of strong nymijhce for the subinternal ligament, and in the full 

 development of the cardinal teeth ; which, though minute, stand sharply 

 out from under the cardinal border, instead of being subobsolete upon 

 its internal face. The ligament falls little short of being entirely inter- 

 nal. So strong, and so strongly attached is it, that all attempts to clear 

 it from the hinge-processes were ineffectual, and their exact shape (which 

 appears to differ slightly in different individuals) could not be made out. 

 In fact, in opening the shell, the valves would usually give way before 

 the ligament. Its attachments appear to be entirely internal, though 

 the edges of the valves do not quite close over its outer surface. The 

 margin of the shell appears perfectly plain, and most of the specimens 

 *)ossess a slender byssus. 



Modiolarca pusilla, Gould, appears (from the type specimens) to belong 

 to this group, but it differs from K. minuta in form, color, and larger 

 proportional size of the teeth. Gould's figure does not well represent 

 his typical specimens. They were from Tierra del Fuego, and among 

 some minutkc from Orange Harbor, collected by the United States Ex- 

 ploring Expedition, T found several specimens of K. minuta. In some 

 respects this shell recalls Ceropsis of the Carditidce. 



I am pleased to be able to connect with this interesting little form 

 the name of Dr. Kidder, who has, with very limited opportunities and 

 the disadvantage of a comparatively short stay on the island, succeeded 

 in accumulating a most interesting fund of specimens and biographical 

 notes. 



MYTILID^. 



Mytilus MAaELLANicus, Ohemn. 

 Mus. No. 11909. 



New Zealand, Straits of Magellan, authors; Kerguelen Island, Dr. 

 Kidder; four living specimens, much eroded, and numerous dead 

 valves. , 



