DISTRIBUTION AND OCCURRENCE OF EURYPTERIDS 501 



said that with further study the Limulava will probably be made an order 

 coordinate with the Eurypterida. This is also the position taken by 

 Clarke and Euedemann (Mem. Eurypt., pages 406-410), who consider 

 that "this order possibly belongs to the Merostomata, but it is distinctly 

 allied to the crustaceans . . . ." and that it is more generalized than 

 the Eurypterida. 



The only true Eurypterid from the Cambric is Strabops thacheri 

 Beecher from the Potosi limestone of Missouri, a formation generally 

 classed as of Upper Cambric age. One almost perfect individual has 

 been found, but it occurs without any other fossil associates in an argil- 

 laceous calcilutyte, the origin of which is not proven to be either marine 

 or non-marine, though associated beds carry a good marine fauna. 



Upper Ordovicic. — From the Ordovicic until just recently only two 

 occurrences had been noted, that of Ecliinognatlius clevelandi Walcott, 

 described from the Utica shale of Holland Patent, New York, where one 

 thoracic appendage and a portion of a thoracic somite were round, and 

 that of Megalograptus welchi S. A. Miller, originally described as a 

 graptolite and occurring with a typical marine fauna, chiefly crinoids, 

 in the Liberty or Middle Richmond beds of Warren County, Ohio. The 

 material consists of fragments of walking legs (one nearly complete) and 

 a few body segments. Lately there have been some extremely interesting 

 discoveries of Eurypterids in the Schenectady and Xormans Kill shales 

 and sandstones of the Mohawk and Hudson valleys. The preliminary 

 notice of the Schenectady specimens (originally referred to the Frank- 

 fort), which has appeared in the report of the Director of the New York 

 State Museum for 1910 (page 31 ), shows that these remains, ''usually m 

 fragmentary condition, abound most freely in fine-grained black shale, 

 intercalated between thick calcareous sandstone beds . . . , but they 

 also occur in the sandy passage beds between the two. The sandy shales 

 are full of organic remains, partly of the supposed seaweed Splienothallux 

 latifolium Hall and partly of what appear to be large unidentified patches 

 of Eurypterid integument. In the black shales the Eurypterid remains 

 are rarer, but their surface sculpture is excellently retained, and here 

 their organic associates are CHmacograptus typicalis and Triarthrus 

 bechi. As a result of imperfect retention of these Eurypterids in the 

 rocks where they most abound and their sparseness in the shales which 

 have best preserved them, we are still left in ignorance of the full com- 

 position of the assemblage, hut it is safe (o Bay genera, species, and indi- 

 viduals were abundant at this early period, and (he evolution o\' dis- 

 tinctive characters . . . had progressed to so sharp a differentiation 

 that we are compelled to carry hack farther in history some of the com- 



