OF CONCHOLOGY. 137 



shaped plate formed by the two laminae, and in ? Mag as patagon- 

 ica there is only a rounded ridge between them. The septum is 

 broad, arising close to the hinge plate, obliquely forward, and is 

 truncate at its extremity, which touches the opposite valve. The 

 reflected loop is broad and quite circular. The cardinal muscles 

 are attached in the apical cavity of the neural valve. The pe- 

 duncle is short and stout, the other muscles are very slender. 



Length -34 in., breadth -32 in., diameter '16 in. 



A single specimen was found adhering by its peduncle to a 

 large specimen of Waldheimia venosa from Orange Harbor, 

 Patagonia. ?"Les isles Malouines," D'Orb., 1. c. 



It is not unlike, in general appearance, a very minute specimen 

 of W. venosa, except that the foramen is much larger, incomplete 

 and of a different shape. It may be identical with D'Orbigny's 

 species, of which the apophyses are not figured, but differs in 

 its small size and rounded form. 



The other species of the genus are as follows : 



Magasella Spitzhergensis, Davidson, P. Z. S. 1852, p. 78. 

 Rve. Conch. Ic. pi. vii, fig. 24. 



Some specimens marked " T. Labradorensis," in the Museum 

 of the Philadelphia Academy, but agreeing with Reeve's figure 

 and descriptions, have the typical loop of Magasella. 



Sah. North Atlantic and Arctic seas, Murray Bay ; Gulf of 

 St. Lawrence, P. P. Cpr. 



Magasella Cumingii, Davidson, P. Z. S. 1852, p. 78, pi. xiv, 

 fig. 10—16. Reeve, Conch. Ic. pi. viii, f. 29. 



Habitat. New Zealand, 



Magasella crenulata, Shy., Thes. Conch, i, p. 858, 1846, pi. 

 71, fig. 96—98. 



This species resembles ? Magas patagonica, Gld., and they 

 may prove identical upon comparison. 



Habitat. "Santa Cruz, Canaries, Cuming," teste Rve., appa- 

 rently with doubt. 



Section KRAUSSININ^. 



Loop entirely absent, apophysary system consisting of two 

 lamellae attached to the prominent mesial septum of the hgemal 

 valve, and laterally extended. 



The external characters of the two genera which compose this 

 section, difi"er widely ; but we have seen that these external at- 

 tributes are of little value, even in the same genus, in many cases, 



