242 THE HABITAT OP THE ETJRYPTERIDA 



Summary of the Wenlock Fauna. A survey of the entire euryp- 

 terid fauna of the Wenlock of Scotland must be made with the reali- 

 zation beforehand that all of the material is so fragmental, dismem- 

 bered, 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 per- 

 ornatus is found abundantly at Lesmahagow, the last variety, how- 

 ever, 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 £. macrophthalmus, and which has not 



