4IO NEW YORK STATE MUSEUM 



The rhabdosomes of C. putillus are so much like the narrow 

 sicular ends of those of C. typical is that it would seem necessary 

 to unite the two, were it not for the fact that in certain layers of the 

 Utica shales (as at Mosher's creek in the Mohawk valley) innumerable 

 specimens of the former species are found, all of which attain a uniform 

 small size, apparently that of the mature form, and that the thecae of C . 

 putillus are still a little longer. 



In Lees gulf near Turin, Lewis co., I have found shales lying probably 

 little below the base of the Lorraine, filled with a mutation of C . t y p i - 

 calis [see pi. 28, fig. 7] that is principally marked by its failure to attain 

 the full width of the type form and the markedly slower widening of the 

 rhabdosome. At a distance of 15 mm (approximately the maximal length 

 of the rhabdosome of this mutation) from the sicula the width is but 1.2 

 mm against 2.2 mm in the type. Also the thecae do not increase materially 

 in size and there are 15 counted in the space of 10 mm throughout the 

 length of the rhabdosome. For the latter reason these can not be merely 

 young rhabdosomes of C . t y p i c a 1 i s ; but they rather appear as rhabdo- 

 somes that have failed to attain mature characters while outyrowinsf the 

 young in size. 



Hall has figured the transverse section of the rhabdosome as concavo- 

 convex. Specimens embedded in Galena limestone from St Paul, Minn., 

 have enabled us to verify this observation. It has been found that the 

 concave or flat side is the obverse and the convex the reverse side. 



This asymmetric section also explains another peculiarity of this species, 

 viz, the different aspects of the thecae on the obverse ami reverse sides ; a 

 difference best seen when a specimen preserved in relief is parti) - broken 

 out, as in the original of figure 355. In the latter the lower thecae appear 

 as narrow vertical tubes, suggesting handles, while in the; impression of the 

 other side they are broad, overlapping and separated by short, shallow 

 apertural excavations. This difference in the two sides is very character- 

 istic of C. typical is and also easily observed in the flattened speci- 

 mens from the Utica shale. Its cause is seen in cross-sections to lie in the 



