MOLLUSCA. 701 



situated in the bottom of a broad, concave, revolving channel. 

 Surface of the volutions between the margins of the sutural 

 channel, nearly flat or slightly convex; marked by four or five 

 strong, revolving costae, the three lower ones being subequidis- 

 tant, the upper one more remote; in the broader interspace be- 

 tween the uppermost strong costa and the one next below, is a 

 much finer rib, and a similar one about midway on the slope 

 from the uppermost strong costa to' the suture, although this last 

 one is sometimes strong enough, especially in the larger shells, 

 to be counted as one of the major ribs; in each of the interspaces 

 between the three lowermost strong costse on the larger volu- 

 tions, there is frequently a much smaller raised line; and on the 

 slope of the lowermost one of these costse to the lower suture, 

 another one somewhat stronger than those in the interspaces 

 above. The surface is also marked by very fine transverse lines 

 of growth. 



Remarks.} Conrad's original illustration of this species is very 

 poor and from it alone the species would not be recognizable. 

 A large number of excellent examples, however, have been ex- 

 amined in the collection of the National Museum at Washington, 

 and the New Jersey specimens do not differ from them specific- 

 ally. The southern specimens show considerable variation in the 

 secondary revolving ribs, but the three strong ribs below, fol- 

 lowed by a broader interspace and then a fourth rib is a constant 

 character of the species. In New Jersey the species is associated 

 with T. marshalltoumensis but is much less common, and is rep- 

 resented by fragments only. The surface markings are suffi- 

 ciently peculiar to render the identification of mere fragments 

 of the shell a comparatively easy matter, but the internal casts 

 would not be materially (different from those of several other 

 species. 



The species should be compared with T. winchelli Shum. 1 , 

 from Texas, a species which has a similar interval between the 

 upper costa and the three lower ones, but the shell of that species 

 is coarser in appearance, the revolving lines broader and stronger, 

 and in some individuals only two strong ribs are present below 

 the interval. 



1 Bost. Soc. Nat. Hist., vol. 8, p. 196. 



