TRENTON LIMESTONE. 123 



1G4. 11. ORTHIS PECTINELLA. 



Pl. XXXII. Figs. 10 a, b, c, d, e. 



OrlJtis callactis & Orthis flabellulum. Conrad, Ann. Geol. Report of 1840, p. 201 ; of 1S41, p. 27. 

 Orthis pectinella. Conrad in M.S. Kmmons, Geol. Report, 1813, pag. 394, ill. ICJ, fig. 2. 

 Compare Orthis callactis, D.4.lman, VeL Acad, llandl. 1S27, pag. 112, pl. 2, fig. 2. 



— — HisiNGER, Pet. Suecica, 1S37, pag. 70, tab. 20, fig. 9. 



— — SowERDY in Murchison's Sil. System, 1839, pag. 613, pl. 19, fig. 5. 

 Orthis flabellulum. J. Sowerby in ib. fig. S ; and pl. 21, fig. 8. 



Orthis calligramma, and synonymy. Murchison and Vkrneuii., Pal. of Russia and the Ural Mountains, 

 pag. 207, pl. 13, fig. 7 a, b, c, d, e,f; %ar. orlhamboniies, fig. 8; var. ovata, fig. 9.* 



Suborbicular or obtusely seraioval, wider than long in the proportion of about 9 to 12 ; 

 cardinal line extended, equal to or less than the greatest width of the shell, slightly deflected 

 at the extremities ; area moderately large and well defined ; shell resupinate, or the area 

 and foramen being principally on the flatter valve, or partially conmion to Ixjlh ; dorsal 

 valve subconvex near the beak, with Hat sides and a broad depression along the centre, 

 which is distinct in front ; ventral valve regularly convex, most prominent in the centre ; 

 beak extending only to the cardinal line ; surface marked with from 22 to 30 prominent 

 rounded radii, which are equal to the spaces between ; radii simple, or bifid and trifid 

 towards the margin, crossed by small elevated concentric lines. 



This shell usually presents a regular suborbicular outline, with well defined dorsal area, 

 and strong diverging ribs, which are well marked to tlie beaks of the shell. A prominent 

 distinguishing trait is its resupinate character, placing the area and foramen essentially on 

 the dorsal valve, which is nearly flat, while the ventral one is convex. The radii, in some 

 specimens, are of uniform size and undivided, while in others they are bifid and trifid from 

 the middle downwards. The number of ribs is greater than in the 0. callactis of Dalman ; 

 and in this respect, as well as their subdivision, it resembles the O. Jlabellulum of J. 

 SowERBY, as cited above. 



Fig. 10. A small individual, having the radii simple on both valves. 



Fig. 10 a. The ventral or convex, valve, with the radii simple or nearly so. 



Fig. 10 h. Dorsal valve of the same specimen, having the radii bifid and trifid towards the margin. 



Fig. 10 c. Cardinal view of another specimen. 



Fig. 10 d. Ventral valve, with the radii nearly simple. 



Fig. 10 e. Interior of the ventral valve. 



Position and locality. This species, though not usually abundant, occurs nevertheless in 

 nearly every part of the Trenton limestone, thougii unknown to me in the Hudson-river 

 group. Its principal localities are Middleville, Trenton Falls, Sugar River, Turin, Water- 

 town, showing that the species is widely distributed. (State Collection.) 



• M. DE Verneuil regards the Orthis calligramma, O. callactis? O.flahclhihim, and others, as being the single 

 species first named by D.-ilm.\n, the other names having been applied to varieties of the same species. The species 

 referred by me to Orthis flabellulum (Report, 1813, pag. 105, fig. 5), is apparently distinct from the one under 

 consideration, and occurs in a liigher position. 



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