236 THE HABITAT OF THE EUEYPTERIDA 



The Upper Siluric Faunas of the Baltic Region. Let us next con- 

 sider 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. rectangular is 

 Schmidt, E. laticeps Schmidt, Pterygotus osiliensis f 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 Ptery- 

 gotus 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 rec- 

 tangular is naturally has its closest affinities with the Bertie forms. 

 Schmidt described E. laticeps from two carapaces and did not com- 

 pare 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. micro phthalmus from the 

 Manlius waterlime. The largest specimen of the latter species meas- 

 ures 30 mm. long by 45 mm. wide, while one of the two known cara- 

 paces 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. 

 micro phthalmus 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. micro phthalmus , 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 closelv related to the Manlius 



6 While it is not the intention of the author of this paper to revise or emend any generic or spe- 

 cific 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. 



