DISTRIBUTION AND OCCURRENCE OF EURYPTERIDS 511 



species. The remains are described chiefly under the genera Eurypterus 

 and Pterygotus, there being, however, an abundance of perfect specimens 

 of Slimonia acuminata Salter from Lanarkshire and one poor specimen 

 of Stylonurus logani Woodward, with some doubtfully determined frag- 

 ments of S. powriei Woodward. There are twelve species of Eurypterus 

 found mainly in the upper beds of the Downton sandstone and occurring 

 in some cases also in the Passage beds to the Lower Old Eed sandstone. 

 The remains are fairly numerous, but nearly always imperfect, there 

 being sometimes one almost perfect representative of a species and then 

 a great many small broken pieces. Some of these are closely similar to 

 American species belonging to the genera Eusarcus and Hughmilleria 

 (Clarke and Euedemann, page 91). These Upper Ludlow sandstone and 

 grit beds, with the Bone bed forming the top and followed by the Led- 

 bury shales, the Downton sandstone, and the Tilestones, have been inter- 

 preted by Geikie as a series of formations indicating a change from ma- 

 rine to land conditions. Eleven species of Pterygotus have been found 

 in various members of the Ludlow group, mainly in the upper part. Be- 

 tween the Downton Castle sandstone and the underlying beds is a grayish 

 layer, sometimes black with vegetable remains, and this contains Ptery- 

 gotus, fresh-water fish remains — forerunners of the Old Red fishes — and 

 numerous Crustacea. The species of Pterygotus are in a very much better 

 state of preservation than are those of any of the other genera found in 

 these beds. That so many species of Pterygotus, including many well 

 preserved individuals and an even larger number of fragments, should be 

 found in this layer, which is often black with vegetal remains and con- 

 tains, besides, fresh-water fish, is indeed significant. The species Ptery- 

 gotus problematicus Salter, already mentioned as occurring in the May 

 Hill sandstone, is also reported from the Upper Ludlow rock of Ludlow, 

 England, from the Ludlow Bone bed at Ludlow, the Downton sandstone 

 at Kington, and the Base of the Old Eed at Ludlow, but it is probable 

 that this species, represented only by fragments, has not such a wide 

 range, the identification of the fragments being incorrect. Geikie notes 

 that "vegetable remains, some of which seem to be fucoids, but most of 

 which arc probably terrestrial, and lycopodiaceous, abound in the Down- 

 ton sandstone and Passage beds into the Old Eed sandstone. The Euryp- 

 terid genera still continue to occur, together will) phyllocarids (Cer&tio- 

 can's) and vast numbers of the Ostracod Beyrichia ( />. kloedeni). Prev- 

 alent shells are Lingula cornea and Platyschisma h elicit es. The Ludlow 

 fishes are also met with." 112 Geikie, furthermore, considers tin 1 oeeur- 



I'-TcxMiook of Geology, 4th edition, 1). 0(51. 



