360 NEW YORK STATE MUSEUM 
this telson we may say that there appears to have existed some variation 
in form, as there is among our specimens one showing the other extreme, 
namely, a relatively broad form [pl. 72, fig. 3]; none of these differences 
seems sufficient for the erection of new species, since the occurrence of 
transitional stages 1s obvious. Moreover, a slight lateral compression which 
clearly has affected some of the specimens, and specially the type of 
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Figure 72 Original figure of Pterygotus Figure73 Pterygotus buffaloensis 
cummingsi Grote & Pitt Pohlman,. The original figures 
acuticaudatus, is fully competent to produce a hke effect [pl. 77, 
hige.s]. Text figure 75 1s a reproduction of the type of P. quadrati- 
caudatus and plate 76 shows the ultimate segment, which in reality 
it is, in position in a nearly complete postabdomen. Finally Pohlman 
cited P. bilobus Huxley and Salter,as among the forms of the 
waterlime at Buffalo, basing his assertion on a fragment consisting of 
eight posterior segments. This fragment is preserved in the museum of 
