TRENTON LIMESTONE. 
123 
164. 11. ORTHIS PECTINELLA. 
Pl. XXXII. Figs. 10 a, b, c, d, e. 
Qrthis callactis & Orthis flabellulum. Conrad, Ann. Geol. Report of 1840, p. 201; of 1841, p. 27. 
Orthis pectinella. Conrad in MS. Emmons, Geol. Report, 1843, pag. 394, ill. 105, fig. 2. 
Compare Orthis callactis , Dalman, Vet. Acad. Handl. 1827, pag. 112, pi. 2, fig. 2. 
— — Hisinger, Pet. Suecica, 1837, pag. 70, tab. 20, fig. 9. 
— — Sowerby in Murchison’s Sil. System, 1839, pag. 613, pi. 19, fig. 5. 
Orthis flabellulum. J. Sowerby in ib. fig. 8 ; and pi. 21, fig. 8. 
Orthis calligramma, and synonymy. Murchison and Verneuil, Pal. of Russia and the Ural Mountains, 
pag. 207, pi. 13, fig. 7 a, b, c, d, e,f; var. orthambonites, fig. 8; var. ovata, fig. 9.* 
Suborbicular or obtusely semioval, 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 common to both ; dorsal 
valve subconvex near the beak, with flat 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 the 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 O. callactis of Dalman ; 
and in this respect, as well as their subdivision, it resembles the O. flabellulum 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 b. 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 c. Interior of the ventral valve. 
Position and locality. Tins species, though not usually abundant,-occurs nevertheless in 
nearly every part of the Trenton limestone, though 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. flabellulum, and others, as being the single 
species first named by Dalman, the other names having been applied to varieties of the same species. The species 
referred by me to Orthis flabellulum (Report, 1843, pag. 105, fig. 5), is apparently distinct from the one under 
consideration, and occurs in a higher position. 
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