STROPIIOMENA. 127 



Warsaw, Nanvoo, St. Clair county, Illinois, &c. In India, at Moosakhail, &c, in the 

 Pnnjaub. It was found also in Spitsbergen, and in Australia, &c, &c. 



Var. A. — Streptorhynciius Arachnoidea, Phillips, sp. PL XXV, rig. 19 — 21, 

 PL XXVI, fig. 2, 3, 4 (lower figs.), 5, 6. 



Spirifer arachnoidea, Phillips. Geol. Yorks., vol. ii, pi. xi, fig. 4, 1836. 

 Orthesina Portlockiana, Semenow. Ueber die Fossilien des Schlesischen Kohlen- 



kalkes, pi. ii, fig. 1, 1854. 

 Ortiiis arachnoidea, Be Verneuil. Geol. of Russia, vol. ii, pi. x, fig. 18, 1845. 



Professor Phillips describes his S. arachnoidea as " very depressed, truncato-orbicular, 

 hinge-line wide as the shell ; striae fine, sharp, and continually subdivided ; upper valve 

 convex, as in S. resupinata.'' This description would certainly suit many specimens of 

 true S. creuistria ; but the figure in the ' Geology of Yorkshire' would not indicate a shell 

 with a convex valve, such as that possessed by the Martins species, and was evidently 

 intended for those very depressed varieties in which the valves were almost flat or but 

 very slightly convex, one of them being even at times a little concave from the middle to 

 the margin, as will be found represented in our PL XXV, fig. 19 — 21 ; PL XXVI, fig. 2, 

 3, 4. Such, at any rate, is the shell we can conceive as having been intended for S. 

 arachnoidea. The area in this is narrow, while the striation is entirely similar to what 

 we have already described. This variety or variation in shape of S. crenistria generally 

 occurs in the same localities where the more convex forms are met with. 



Professor Phillips mentions Stradon, Haltwhistle, Allenheads, near Heskel Newmarket. 

 It is found also at Rutcheugh, and other places in Northumberland; in Scotland, in 

 the localities already enumerated ; while in Ireland, it occurs at Curragh, Ardmore, Kildare, 

 Kildress, &c, &c. 



Var. B.— S. Kellii, WCoy. PL XXVII, fig. 8. 



Orthis Kellii, M'Coy. Synopsis of the Characters of the Carboniferous Fossils of 



Ireland, p. 124, pi. xxii, fig. 4, 1844. 



In shape, this species or variety ? is marginally semicircular and slightly indented in 

 front, the hinge line being a little shorter than the greatest width of the shell. Ventral 

 area narrow, and divided by a triangular fissure covered by a pseudo-deltidium. The 



