4 
DEVONIAN FAUNA. 
2. Genus. — Allorisma, King, 1844. 
These shells are elongate, very thin, equivalve, edentulous, and very inequi- 
lateral, with elongated ligamentary supports, and with concentrically plicate and 
finely punctate surfaces. They range from the Devonian to the Pernian. 
1. Allobisma dtjbium, Whidborne, sp. PI. I, figs. 2, 2 a, 3. 
1889. Edmondia ? dubia, Whidborne. Geol. Mag., Dec. 3, vol. vi, p. 79. 
Description. — Left valve long, rather narrow, ovoid, slightly convex. Umbo 
small, incurved, very anterior, turned forwards, oblique, depressed below the 
greatest altitude. Lunule small, deep, undefined. Area narrow, concave, deep. 
Anterior margin small, very convex. Inferior margin slightly oblique and 
convex. Hinge-margin slightly convex. Shell-structure papyraceous. Surface 
covered with numerous, very fine, sharp, regular, close, bifurcating growth-strise, 
and (on the internal cast) with very low indistinct radiations. 
Size of valve. — Breadth 34 mm., depth 14 mm. 
Localities. — An imperfect specimen from Wolborough is in Mr. Vicary's 
Collection, and a still more defective shell from Lummaton is in my Collection. 
Remarks. — Mr. Vicary's specimen has lost the posterior portion, and is 
another of the many fossils from these localities which rather prove the existence 
of a species than enable us to describe it. 
It appears to come so near to Allorisma sulcatum, Fleming, sp.,^ as in all 
probability to belong to the same genus, while it differs specifically in being 
much less elongate, and in its ornament being finer. The radiations mentioned 
above probably indicate the punctate lines which characterise this genus. 
De Koninck's genus Broehia^ also presents characters to which it approaches. 
Affinities. — From Edmondia coelata it differs by being much flatter and broader, 
by having a differently shaped umbo, the posterior boundary-line of which is 
much sharper and more defined, and overhangs the hinge-margin so as only to 
leave room for a narrow conoave area, and by showing signs of radiation. 
» 1836, Phillips, ' Geol. Yorks.,' pt. 2, p. 209, pi. v, fig. 5 ; and 1884, Tryon, ' Struct. Conch.,' 
vol. iii, p. 148, pi. cvii, fig. 44. 
2 1885, de Koninck, 'Ann. Mus. Eoy. H. N. Belg.,' vol. ix, pt. 5, p. 19. 
