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 is 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 cummingsi Grote & Pitt | Figure 73 Pterygotus buffaloensis Pohlman. The original figures |
acuticaudatus, is fully competent to produce a like effect [pl. 77, fig. 5]. Text figure 75 is a reproduction of the type of P. quadraticaudatus 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
