The Upper Siluric Faunas of the Baltic Region. Let us next consider the fauna from Oesel, Gotland, and the Baltic provinces of Russia. On Oesel three species and two varieties of eurypterids are known: Eurypterus fischeri Eichwald, E. fischeri var. rectangularis Schmidt, E. laticeps Schmidt, Pterygotus osiliensis,[1] Schmidt, and P. osiliensis var. laticauda Schmidt. From Gotland the same Pterygotus species is reported, but no Eurypterus has yet been found. In Podolia a few specimens of Eurypterus fischeri, fragments of Pterygotus osiliensis occur, and Schmidt reports a few broken pieces of shell referable to the latter species in Galicia. From Livland, Pt. osiliensis has been reported by Eichwald. It is thus seen that in the Baltic Isles and West Russian provinces three species and two varieties of eurypterids occur. The close similarity, approaching identity, of Eurypterus fischeri to E. remipes and E. lacustris from the Bertie has been dwelt on at length (p. 230 above); the variety E. fischeri rectangularis naturally has its closest affinities with the Bertie forms. Schmidt described E. laticeps from two carapaces and did not compare it with any other form. There is no species in the Siluric fauna of Great Britain to which it shows any relationship, and so far as I am aware it cannot be compared with any other European form; but it shows considerable resemblance to E. microphthalmus from the Manlius waterlime. The largest specimen of the latter species measures 30 mm. long by 45 mm. wide, while one of the two known carapaces of E. laticeps shows corresponding measurements of 40 mm. and 60 mm., the ratio in both cases being as 2 to 3. The form of the eyes corresponds quite closely in the two species, but whereas in E. microphthalmus the distance between the eyes is almost equal to that between the eye and the lateral margin, in E. laticeps, on the other hand, the eyes are more widely spaced so that the distance between the eyes is one and a half times as great as between each eye and the margin (Schmidt, 248, 63). No ornamentation has been observed on the carapace of E. microphthalmus, but on E. laticeps a series of black dots occur in rather regular arrangement between the eyes, extending forward toward the frontal margin and posteriorly a shorter distance. Since both of these species are as yet so little known, it is not safe to draw conclusions as to their relations. The fact of chief interest is that the Baltic form is more closely related to the Manlius
- ↑ While it is not the intention of the author of this paper to revise or emend any generic or specific appellations of other authors except in so far as is necessary in the discussion of the problem at hand, it is advisable to call attention to the fact that Pterygotus osiliensis belongs to the subgenus Erettopterus established by Huxley and Salter for the Pterygoti which have bilobed telsons.
