BRITISH SILURIAN BRACHIOPODA. 131 



and especially prominent at the umbo ; a rounded longitudinal elevation extends from 

 the umbo to the front, giving the valve a somewhat roof-shaped appearance. Surface of 

 valves smooth, marked only by a few concentric lines of growth. 



Length 9, width 7, depth 6 lines ; but in some specimens the length and breadth 

 are nearly equal. 



Obs. — We have already given the characters of the spiral and of its attachments. It 

 has not been hitherto found in our British Silurian Rocks, and is here briefly described 

 on account of its being the type of the genus Hindella. 



It is not a rare fossil at Junction Cliff, Anticosti ; and the strata there are higher in 

 the geological series than the Cincinnati group, and come between that and the Clinton 

 strata. 



Genus — Ambocceija, Hall, 1860. 



(A/i/3a)»', umbo ; and KoiXia, venter.) Type Orthis umbonata, Conrad. 



In the 'Thirteenth Annual Report of the Regents on the State Cabinet,' 1860, Prof. 

 Hall proposed a new genus, Amboccelia, for a shell described by Conrad in the 

 'Journal of the Academy of Natural Sciences,' vol. viii, 1842, under the name of Orthis 

 umbonata, and occurring in tlie Devonian or Hamilton group at Moscow, New York State, 

 and in the same rocks at Seneca Lake on the shores of Lake Erie. He adds that 

 Spirifera unguiculus of Sowerby may likewise be included in this genus. 



Prof. Hall describes the external characters of his genus, and gives figures of the 

 internal surface of both of its valves ; but says nothing with respect to its spirals. These 

 have been clearly worked out by the Rev. Norman Glass in two or three specimens ; and 

 he found them to be similar to those of Spirifera proper, each spiral cone being 

 composed of five convolutions. 



The external shape and characters of the type of this genus are peculiar. It is 

 marginally somewhat subpentagonal ; hinge-line nearly equals the greatest width of the 

 shell. Dorsal valve is convex at the umbo, after which it becomes slightly concave to the 

 margin with a narrow false area. The ventral valve is very convex, and divided 

 longitudinally by a median groove ; beak large, produced and incurved at its extremity ; 

 area large, divided by a triangular fissure; surface of valves smooth. 



The species referred by Hall to his genus are small, the type measuring — 

 Length 6, breadth 5^, depth 4 lines. 



In Great Britain the genus may be represented by the Sp. Urei (Carboniferous) =: 

 Sp. unguiculus. Sow. (Devonian), and = Sp. clannyafia. King (Permian). All these shells 

 partake of the same characters, and to my eye are specifically indistinguishable. They 



