1916.] NATURAL .SCIENCES OF PHILADELPHIA. 377 



and white, though the corrugations arc more or less tinged with 

 slate color. The visceral hump i^ enormous, subglobular, shorter 

 than the foot, height above the sole 52 mm.; above the sulcus 

 between mantle-edge and foot 40 mm.; longitudinal diameter 

 42 mm.; transverse diameter 37 mm. The hum]) is largely covered 

 by a thick, obscurely pustulous, almost coriaceous layer (the notaeum) 

 beneath which is a thin, transparent but quite tough mantle which 

 in spirits expands below the basal edge of the not a 'inn above the pedal 

 sulcus especially in front (though not as much as in 0. corys), like 

 a mass of bubbles, with a hardly perceptible sinus on either side 

 forming an incurrent and an exhalent channel, which however does 

 not affect the margin of the notaeum, the latter being entire except 

 for a slight incurvation in the median line in front. 



The summit of the notseum (in spirits) exhibits an ovoid foramen 

 about 30 mm. long by 24 mm. wide, through which the shell, covered 

 by the excessively thin transparent mantle, is partially visible. 



There is a transverse slit-like opening between the mantle and 

 the pedal sulcus, directly behind the head, in which the osphradium, 

 ctenidium and excretory outlets are situated. The osphradium is 

 of a greenish tint, with darker margins. The gill is translucent 

 white. In the former the filaments are single and elongated on 

 either side of the stalk, not short and double as in 0. corys. The 

 ctenidium has a single row of long, triangular, not auriculate lamellae 

 much as in that species. 



The jaw much resembles that of 0. corys, but the radula was so 

 deeply retracted that it was thought best not to break up the unique 

 specimen by cutting to extract it. 



The base of the arc of the shell measures 40 mm. long by 32 mm. 

 wide. It has much the shape of the bowl of a deep oval ladle and it^ 

 depth is about 15 mm. when in normal position. Its structure i- 

 concentric, not in circles but in a rounded-quadrate fashion. On 

 the edge of the left side behind is a knot-like nucleus. On the inner 

 surface near this nucleus and extending for a length of about 12 mm. 

 away from it are two elevated straight ridges, which at half then- 

 length from the nucleus join to form a single stronger ridge which 

 gradually diminishes and becomes obsolete on the inner surface of 

 the disk. The appearance of these ridges suggests that if the shell 

 was spirally coiled they would form a columella. The outer surface 

 of the shell, to which the mantle adheres tenaciously, is smooth, but 

 undulated by more or less irregularly disposed concentric wrinkles. 

 It is attached to the body only by a small area at the edge near the 



