238 THE HABITAT OF THE EURYPTERIDA 



that of the latter. The similarities, however, are pronounced, and 

 it is not to be denied that P. osiliensis finds its nearest relative in 

 P. bilolus. Aside from this species, there are several others belong- 

 ing to the subgenus Erettopterus, and we cannot dismiss our com- 

 parative study without calling attention to them. They are: Ptery- 

 goids {Erettopterus) grandis, and globiceps from North America; but 

 they are so very distinct from the Baltic form that genetic relation- 

 ship is in no way indicated. 



The variety laticauda of P. osiliensis is founded not without cer- 

 tain misgivings on the part of Schmidt for an exceptionally large 

 metastoma and a similarly large telson found associated with the 

 P. osiliensis specimens. So far as the present problem of the deter- 

 mination of the relations between faunas is concerned, this variety 

 would be classed along with P. osiliensis, and needs no separate dis- 

 cussion. 7 



The species of faunas of the Upper Siluric waterlimes of Oesel, 

 Gotland, Livland, Podolia, and Galicia are thus seen to show very 

 close relationship either to species in the Bertie waterlime, as in the 

 case of Eurypterus fischeri, and var. rectangular is, or to species found 

 in Great Britain at the end of the Siluric or the beginning of the 

 Devonic. That is, they show affinities to the faunas occurring in 

 deposits which for reasons other than faunal ones were judged to 

 have been derived from the continent of Atlantica. 



The Fauna of the Wenlock. There now remains only the dis- 

 cussion of the eurypterid-bearing deposits of Great Britain, (6) the 

 Wenlock of Scotland, and (7) the Old Red sandstone. In the Wen- 

 lock beds there is a large fauna represented by at least twelve deter- 

 minable species of eurypterids, and one would expect to be able to 

 attain to some critical knowledge of the relationship of the forms there 

 occurring to those in North America and Europe ; but while the fauna 

 lacks not in the number of species and of individual remains, com- 

 plete or even nearly complete specimens are not to be found, and 

 one is forced to attempt to draw conclusions concerning relationships 

 from fragments of legs, carapaces, or body segments, an attempt which 

 is not only difficult but altogether unsatisfactory because of the prob- 

 able errors attending it. Let us, however, consider the species 



7 The author, however, questions the propriety of the creation of a new variety for the two speci- 

 mens found. Undoubtedly the metastoma which Schmidt cites is larger than the two which he con- 

 siders belong to the typical P. osiliensis; on the other hand, it is only slightly larger than would be 

 required to fit with the operculum or with the thoracic segment which he figures on Plate V, figs, i 

 and 3. The three metastoma are so similar in form and ornamentation that it seems rather danger- 

 ous to use mere variation in size, particularly when that is so expectable, and when various parts of 

 the body indicate a species of no mean dimensions. 



