Salter and P. banksii Salter and also those of H. socialis." The reference to Hughmilleria in this connection appears to us especially significant, since the eyes show the distinct angulation on the inner side, so characteristic of that genus, and moreover fail to exhibit any signs of the facets, generally quite distinct in Pterygotus. It is quite possible that this specimen is a very large carapace of Hughmilleria partly doubled upon itself in front (of which there is evidence along a break); although on the other hand it must be conceded that the lateral eye is relatively larger than that of H. socialis.
So far then as concerns this carapace P. monroensis is an uncertain species, but unmistakable evidence of the presence of a true Pterygotus in the Pittsford shale is afforded by the free ramus of a chela,[1] reproduced in plate 70, figure 3. Sarle has separated this and a metastoma[2] [pl. 70, fig. 4] on the ground that they belong to coarse-scaled fragments that represent another species. Inasmuch as the carapace as a rule has a much finer sculpturing than the rest of the body (e. g. in P. macrophthalmus), there seems little ground to assume the presence of more than one species of Pterygotus in the Pittsford beds.
Judging from the ramus of the chelicera, this type was more closely related to P. cobbi than to any other form, the latter species possessing the same rounding of the extremity of the ramus and similar form and direction of the teeth [pl. 77, fig. 6], the latter being still a little more rectangular upon the shaft than in P. cobbi.
- ↑ Sarle's description of this reads:
The shaft is nearly parallel sided, 3 mm broad and 12.5 mm long and curves at the end into a stout, striated, nearly perpendicular mucro 3.5 mm long. Back of this mucro is a series of 10 erect, sub triangular, striated denticles, very slightly separated at their bases. They are of three sizes, the largest or primaries being about one half the length of the mucro, the secondaries one half that of the primaries and the tertiaries about one half that of the secondaries. The first primary is separated from the mucro by a secondary and from the second primary by two secondaries and two tertiaries alternating; following the second primary are two secondaries separated by a tertiary. - ↑ Described as follows: An ovate metastoma 27 mm long and 16 mm wide, broadest just anterior to the middle, with the anterior corners slightly truncated, the lobes small and the terminal notch very narrow and shallow. It is marked by coarse, rounded, lobelike scales and is very much more robust than would be expected in Pterygotus monroensis. Judging by the ornamentation, it should be associated with the coarsescaled fragments most frequently found.
