Page:The Habitat of the Eurypterida.djvu/250

242 Summary of the Wenlock Fauna. A survey of the entire eurypterid fauna of the Wenlock of Scotland must be made with the realization beforehand that all of the material is so fragmental, dismembered, macerated, and poorly preserved that detailed descriptions, accurate measurements, and unimpeachable determinations are things beyond the power of anyone to obtain, and that, furthermore, until discoveries of new faunas at earlier horizons in Great Britain shall be made, the ancestry of the Wenlock species must remain obscure. Many new genera appear suddenly in this Lower Siluric horizon, and we are unable to do more than say that such and such genera came from a common ancestor. It is unfortunate, indeed, that the Ordovicic of Great Britain has not yielded such faunas as it has in America. Yet, keeping these points in mind, we are still struck by the provincial character of the Wenlock fauna. There is not a species in it which is closely related to any of the North American species except Eusarcus scoticus which foreshadows in certain respects E. scorpionis from the Bertie.

The Fauna of the Ludlow. The Ludlow of Lanarkshire has yielded nine species of eurypterids. Slimonia acuminata Salter has just been mentioned in connection with S. dubia, the two being very similar. S. acuminata, Clarke and Ruedemann state, "has all the features of a local and aberrant type," (39, 130). Pterygotus (Erettopterus) bilobus with the four varieties: acidens, crassus, inornatus, and perornatus is found abundantly at Lesmahagow, the last variety, however, being very rare. As was pointed out in the discussion of the Baltic provinces faunas, there is closer relationship between P. bilobus inornatus and P. osiliensis than there is between either of these forms and a species in any other fauna (p. 238 above). Stylonurus logani belongs to the revised Stylonurus sens. strict., having the second and third pairs of legs short, thick, and with two pairs of spines in each segment (see Woodward, 312, 131). There are no known species on any other continent to be compared to this form which is not even very much like any of the Wenlock species, with two of which it agrees in its subgeneric characters, but with neither of which it has specific similarities. Indeed, it is quite unlike S. macrophthalmus which is characterized by the peculiar ear-shaped epimeral expansions, the long parallel-sided metastoma, the rounded cephalon, and very short second pair of legs. It is a little more like S. ornatus which has a slightly more squarish cephalon than S. macrophthalmus, and which has not