128 THE HABITAT OF THE EURYPTERIDA 



It is readily seen that a startling conclusion must be drawn from the 

 data, namely, that the Llandovery is not a time period separate from 

 the Tarannon, but that the two are synchronous, the Llandovery being 

 equal in age to the lower Tarannon and appearing as a wedge which 

 widens southward till it reaches its maximum thickness of 96 feet in 

 the Moffat region. The Llandovery is a black mud facies contain- 

 ing a mixed Ordovicic and Siluric fauna, the evidences of the pres- 

 ence of the latter being indicated by the numerous species of Mono- 

 graptus, the Ordovicic aspect being supplied by the Didymograptus 

 species. 



The terrestrial origin of the Tarannon has been shown by two 

 different and mutually independent lines of evidence. It is of inter- 

 est, then, to find in the Upper Tarannon the fragment of a eurypterid. 

 Near the southern border of the Central Belt just south of Bowden 

 which is northeast of Selkirk, there is recorded the occurrence, in the 

 grey blue shales and flagstones probably of the Hawick series, of the 

 telson of Eurypterus and a fragment of Dictyocaris associated with 

 crinoid stems. The typical Hawick rocks found in the neighborhood 

 of Selkirk and further south at Hawick are themselves barren of all 

 fossils but trails, burrows, and tracks. Near Selkirk Crossopodia 

 and Myrionites have been found, while at Hawick Protovirgularia, 

 Crossopodia, Menertites, Nereites and other tracks are abundant and 

 the body segments of a Ceratiocaris have been found. The occur- 

 rence of the single eurypterid fragment in this great barren series 

 is difficult to explain as a marine organism. It may be argued that 

 the presence of crinoid stems is clear enough evidence of the marine 

 nature of the deposits, but such disjointed stems might be washed 

 out from an earlier deposit or even if of the same age as the euryp- 

 terid it is well known that those joints are swept great distances 

 from the original habitat of the crinoids, and that they might be 

 washed far inland on low-lying flats along the shore. At any rate, 

 the single eurypterid remain fails to prove anything definite ; it might 

 be washed in from the sea, but then one must ask why the euryp- 

 terids are not found in the Tarannon muds in the regions where 

 abundant graptolite faunas have been found. The fluviatile origin 

 of the Tarannon has been amply shown, and it is easy to understand 

 on the supposition that the eurypterids were living in the rivers, that 

 fragments of the exoskeletons should be washed out from time to 

 time. It may here be suggested that a further careful search in the 

 Tarannon rocks might well yield a eurypterid fauna as fine and as 



