NAPLES FAUNA IN WESTERN NEW YORK, PART 2 335 



palaeotrochus H all. 1 8 79 

 This term was introduced by Professor Hall as an expression of con- 

 viction rather than of demonstration that the paleozoic shells bearing the 

 aspect of the recent Trochus would eventually prove unlike these in some 

 undetermined features. No one has yet brought forward very satisfactory 

 evidence of such differences, though a considerable variety of names has 

 been introduced for the ancient forms which so closely resemble Trochus 

 and Turbo. Therefore the term Palaeotrochus still serves only to indicate 

 a presumptive distinction. The name was applied to a shell of very 

 different aspect from that here described, and, in the event of the establish- 

 ment of a subordinate division of these genera, it would be probably found 

 necessary to restrict Palaeotrochus (P. kearnyi Hall, Onondaga lime- 

 stone) to exclude such shells as P. prae cursor. In the original descrip- 

 tion of the latter I employed the generic term with the same reservation as 



now. 



Palaeotrochus praecursor Clarke 



Plate 19, fig. 17-26 



Palaeotrochus p r ae c u r s o r Clarke, U. S. Geol. Sur. Bui. 16. 1885. p. 55, 

 pi. 3, fig. 6-9 



Shell of moderate size, turbinate or trochiform, whorls five to six, with 

 early volutions convex, while the final whorl is often obliquely flattened and 

 depressed beneath. The hight of the aperture is five eighths that of the 

 shell. Apical angle about 8o°. Suture impressed, whorls overlapped for 

 more than one half their hight. Aperture subcircular or slightly elongate 

 vertically, outer lip thin, entire, inner lip excavated without callosity, but 

 forming a smooth subspiral surface depressed medially and thickened at the 

 inner and outer edges. Shell nonumbilicate. 



Surface covered with beadlike tubercles arrayed in spiral rows. In 

 adult shells there are from 10 to 15 of these rows, of which that nearest 

 the suture is most conspicuous and composed of the largest tubercles. 

 This row is separated from the suture by an impressed or flattened area. 

 Another strong row occurs at the periphery of the whorl. These tubercles 



