426 CARBONIFEROUS LAMELLIBRANCHIATA. 



the Calderwood Limestone, Kirktonbolm, Kilbride ; the Limestone of Docra, 

 Beith ; Lower Limestone series. 



ObservaMons. — M'Coy founded his species of Sanguinolites variabilis on tAvo 

 very distinct shells, one of which, from its possession of a sinuated pallial line, 

 does not even belong to that genus. It is difficult to understand why these two 

 shells were confused, as they differ so markedly in shape, contour, and surface 

 markings. 



I have found in Mr. Noilson's Collection three other specimens which agree 

 with the more elongate of M'Coy's types. Two of these specimens show the 

 sinuated pallial line of AUorisma, to which genus I now refer M'Coy's shell. 

 Thanks to the authorities of the Woodwardian Museum, Cambridge, I have 

 re-figured M'Coy's two types side by side, PI. XLIY, figs. 1 and 2, to emphasise 

 the differences between them. The rounded posterior end of A. variabilis is in 

 marked contrast to the truncate, oblique, almost straight margin of S. variabilis' 

 Indeed, it will be noted at once that in every detail the shells are different. 



A. variabilis differs from A. sulcata in the less regular character of the 

 concentric grooves and ribs. The two species have a somewhat different contour, 

 A. sulcata being more regularly oval, less oblique, and not curved on itself from 

 before backwards. A. variabilis also attains a much larger size than A. sulcata. 



Allorisma MONENijis, sj). uov. Plate XL VIII, figs. 12 — 14. 



Specific Characters. — Shell of medium size, very inequilateral, obliquely tumid, 

 oblong-ovate. The anterior end is short, deep, and swollen, its margin regularly 

 and bluntly curved. The inferior margin is prolonged, almost straight, or with a 

 shallow sinus about its centre, curving upw^ards posteriorly to pass with a 

 bluntly rounded curve into the posterior margin. The posterior border is very 

 obtusely but regularly rounded. The hinge-line is slightly arclied in front, 

 prolonged and straight behind. The umbones are moderately large, tumid, 

 incurved and pointed, elevated above the hinge-line, and contiguous ; situated 

 in the anterior fifth of the valve. Passing downwards and backwards from 

 the umbo to the postero-inferior angle is a blunt oblique tumidity, which 

 marks off the large, elongate, and compressed dorsal slope from the rest of 

 the valve. This oblique gibbosity is more angular in the neighbourhood of 

 the umbones, and gradually becomes flatter as it passes across the valve; the 

 line of its obliquity is not straight, but curved, being concave upwards. In 

 front of this gibbosity the valve is constricted by a well-mai'ked sinus, shallow 

 above, and becoming broader as it approaches the inferior margin. The lunule is 



