216 EOCENE MOLLUSCA. 



a row of numerous, obliquely compressed, small, knob-like tubercles. The whole surface 

 of the whorls is covered with very fine, slightly undulating, closely set, thread-like, 

 concentric raised lines, irregular, unequal, and roughened by the lines of growth ; these 

 lines are prominent on the canal and the front part of the shell, but become more and 

 more faint, and at last are almost effaced as they approach the shoulders of the whorls. 

 The posterior margins are wide, very slightly channeled along the middle, and orna- 

 mented with numerous slender, concentric lines, four or five of which, running along 

 the sutural edge, are more prominent than the rest, and are decussated by the oblique 

 lines of growth of the sinus, forming a riband-like border to the whorls. The aperture 

 is of an oblong, oval form, and terminates in front in a long, straight canal ; the outer 

 lip is thin, sharp-edged, and much arched ; the sinus is deep, not very wide, and placed 

 a little in front of the middle of the collar. 



In the variety nana (Tab. XXVII, fig. 9), which is proposed for an immature 

 specimen from Colwell Bay, in my collection, the shell is much smaller and narrower, 

 and, apparently, the canal is more produced; but on this last point I cannot speak 

 with certainty, as the canal is not perfect in any of the specimens of the type I have 

 seen. In the general form of the shell, however, in the nearly conical spire, the 

 character of the ornamentation, the position and shape of the sinus, and the roundedly 

 arched outer lip, the specimen in question agrees so exactly with the true P. cymcea, 

 that I can only regard it as a variety of that species dwarfed by unfavorable con- 

 ditions. 



This Pleurotoma, which at first sight might be considered to be a local variety of 

 P. denlata, is distinguishable from that species by the greater width of the shell, the 

 more conical spire, the wider posterior margins of the whorls, the character of the 

 transverse ornamentation, and the numerous small, knob-like tubercles which take the 

 place of the sharp-edged transverse teeth, characteristic of P. dentata. It more resem- 

 bles P. transversaria, as well in the shape and relative proportions of the shell, as in 

 the form and position of the sinus and the character of the concentric lineation ; and 

 a larger series of specimens may eventually lead to the conclusion that it is merely a 

 variety of that species. The tuberculated and sharply angulated whorls, however, 

 characters to which I am not aware that P. transversaria offers any approach, appa- 

 rently entitle the shells in question to specific distinction. 



Size. — Axis, 1 inch and 4-12ths; diameter, \ inch. 



Locality. — Brockenhurst and Colwell Bay, at each of which places it appears to be 

 very rare. 



