302 



Ventral valve moderately convex, most prominent in the middle longitu- 

 dinally, and sloping rapidly downward and outward on each side, its umbo 

 and beak prominent and lightly incurved, the latter truncated and widely 

 perforated : foramen large, circular : deltidium apparently very short and 

 rather wide, but not well shown in any of the specimens that the writer 

 has seen. Dorsal valve flatter, with a much smaller and less prominent 

 umbo and beak than that of the ventral. 



Surface marked by fine concentric strise of growth. On the umbonal 

 region of the dorsal valve of one specimen, also, there are remains of 

 minute radiating strife. Lower layer of the test minutely and densely 

 punctate. Muscular scars of the dorsal valve elongated and narrow, 

 those of the ventral valve unknown. Loop and hinge dentition also 

 unknown. 



Dimensions of the largest specimen collected : greatest length about 

 fifty-six millimetres; maximum breadth, forty nine mm.; greatest thick- 

 ness through the closed valves, twenty-eight mm. 



East end of Maud Island, C. F. ISTewcombe, 1895 : a slightly distorted 

 cast of the interior of both valves, with portions of the test preserved and 

 showing the muscular impressions on the dorsal valve. North side of 

 Maud Island, C. F. Newcombe, 1897 : a cast of the interior of a ventral 

 valve with a small piece of the test preserved. These and the two (not 

 three) " broken and badly preserved specimens " described on page 84 of 

 the first part of this volume, which are probably also from Maud Island, 

 are all that the writer has seen. 



Rhynchonella obesula. (N. Sp.) 



Plate 39, figs. 3, 3 a, and 4. 



{?) Tcrcbratella obcsa (Gabb), Whiteaves. 1884. This volume, part 3, p. 245. 



Shell transversely subelliptical, much broader than long and rather 

 strongly convex when adult, but ovately subtriangular, fully as high as 

 broad and flatter when young, — with no distinct fold or sinus. Umbo 

 and beak of the ventral valve moderately prominent, its hinge area un- 

 known : umbo of the dorsal valve much less prominent, its beak 

 strongly incurved. 



Surface of each valve marked with from twelve to sixteen comparatively 

 large and sharply angular, radiating ribs, with two or three smaller and 

 much less distinct ones on each side. Hinge dentition and muscular im- 

 pressions unknown. 



South side of Alliford Bay, — and north side of Maud Island, Dr. G. M. 

 Dawson, 1878 : the specimens doubtfully referred to Terebratella obesa, 



