BUFFALO SOCIETY. OF NATURAL SCIENCES 



249 



existing between the genera and species of different faunas in order 

 to determine from which continents these were derived, it is evi- 

 dent that a claim of close similarity between a species in the Shawan- 

 gunk fauna, derived as I believe from Appalachia, and a species in 

 the Old Red sandstone derived from the continent of Atlantica, as 

 I hope to prove, must be carefully investigated. Therefore, I proceed 

 to the points enumerated, always bearing in mind that certain types 

 of similarity are of more value than others. In the beginning I may 

 state that S. myops is known only from immature specimens, most 

 of which are carapaces alone, and that only one entire specimen has 

 been found and this is but 55 mm. in length (see pi. 52, fig. 6, Clarke 

 and Ruedemann) . The largest carapace of S. myops observed meas- 

 ured 19 mm. in length by 27 mm. in width; the only carapace of S. 

 scoticus known measured 16 cm. in length and 19 cm. in width; the 

 single, entire individual known measured 3 feet, 4 inches in length. 

 A most profound difficulty arises at once, namely, that of comparing 

 neanic and nepionic specimens of a mid-Siluric species with a gerontic, 

 or perhaps a late ephebic individual of the Lower Devonic. But grant- 

 ing that such comparisons are possible or even allowable, let us turn 

 to the characters which would justify placing these two species in the 

 same subgenus. First, there is the outline of the carapace. It must 

 be admitted even by Clarke aud Ruedemann that, with all due allow- 

 ance for compression, the carapaces of S. myops display a most 

 unusual amount of variation in outline, some, were it not for the 

 position of the eyes, being easily referable to Eurypterus. The cara- 

 paces show a strong tendency to grow narrower posteriorly, showing 

 the greatest width in the anterior third, whence the lateral margins 

 slope gently backwards; the nearly parallel sides shown in the carapace 

 of S. scoticus are usually not present in 6". myops, while the frontal 



S. myops, smallest carapace observed. . 



S. myops, type 



S. myops, largest carapace observed . . . 



S. monophthalmus (Ludlow) 



S. powriei 



.S'. scoticus (separate carapace) 



.S'. scoticus (carapace attached to body) 



LENGTH OF 

 CARAPACE 



IN MM. 



BREADTH OF 

 CARAPACE 



3-5 



5-5 



12.3 



16.5 



19.0 



27.0 



51.0 



61 .0 



50.0 



62.0 



160.0 



190.0 



204.0 



242.2 



ratio: 



length: 



breadth 



0.63 

 0.74 

 o. 70 



0.83 

 0.80 

 0.84 

 0.83 



