MACROCYCLIS. 55 



The species is very nearly allied to M. concava. The differ- 

 ences observable are the following : the size of this shell greatly 

 exceeds the latter in all its proportions, its transverse diameter 

 being nearly twice as great. This difference is not caused by an 

 increased number of whirls, for the number in both is precisely 

 the same ; but this shell seems to be projected originally upon a 

 larger scale, the nucleus being as much larger as mature speci- 

 mens. The color is much more yellow. The umbilicus is not so 

 widely expanded, and does not admit of counting all the whirls ; 

 and the whirls seem to be more voluminous. The strife of growth 

 are usually coarser, and the microscopic revolving striae are 

 stronger and much more constantly present. 



It also strongly resembles 31. sportella, but in that species the 

 revolving lines usually merely cut the summits 

 of the radiating striae, without being continuous ^'8- 9-'- 



over the whole surface. 



Jaw crescentic, ends sharply pointed ; anterior 



„ . , , . ii -ii Jaw of Macrocyclis 



surface ridged ; concave margm smooth, with a ^.ancouverensis. 

 median projection. 



Lingual membrane with 35 arched rows of 43 teeth each 

 (21 — 1 — 21) ; centrals small, ? ; laterals none ; uncini long, 



Fig. 93. 



Lingual dentition of Macrocyclis vaneouverensis. 



narrow, aculeate, recurved, thorn-like, greatly modified in size 

 as they pass off laterally. 



Animal short posteriorly, subcylindrical, very light colored, 

 giving a straw-colored reflection, sides pearly, marked with 

 longitudinal lines of coarse, elongated, squamose granules, about 

 eight or ten on each side. 



