^ 



252 PALJJONTOLOQY OT NKW-TOHK. 



440. 22. ORTHIS ELEGANTULA. 



Pl. LII. Fig. 3o-r. 



OrtU* elegantula. Dalman (not Von Buch), K. Vel. Acud. Handl. 1827, pa-. 117, tab. 2, 

 ftg. 6 a - e. 

 — — HistNGER, Pet. Suecica, pag. 71, tab. xx, fig. 13 a, b, c. 



O. canalis. Sowkkby : Mdrchison, Sil. System, 1839, pag. 631, pl. 13, fig-. 12. 



O. canalis. Hall, Geol. Rep. 4th Dist. N. York, 1843, pag. 107 ; fig. 6, p. 105. 



Compare O. dtgantulal var., page 57, pl. 20, fig. 7, of this volume. 



Shell semioval ; ventral valve nearly or quite flat, sometimes with a depression along the 

 centre ; dorsal valve very convex, extremely elevated towards the beak, which is much extended 

 and incurved over the area ; hinge-line shorter than the width of the shell ; area narrow, not 

 extending to the extremities of the hinge-line ; surface covered with fine stria;, which are 

 dichotomous towards the margin and arched towards the hinge-line. In the more perfect speci- 

 mens, the diverging striae are crossed by extremely fine concentric strife. 



This species is closely allied to O. iesiudmaria, and perhaps more nearly to 0. parva, both 

 of which are lower silurian species. In our specimens, however, the shell is usually more elon- 

 gated and the beak more extended, while the surface is more finely striated, so that there is 

 usually little difficulty in distinguishing it. It occurs in the Clinton group, though usually not 

 in well preserved specimens, and in such a condition that it is not always easy to distinguish it 

 from 0. testudinaria. 



M. DE Verneuil cites this species from Perry county, Tennessee, which is in the same 

 geological position. In the Delthyris shaly limestone of New-York there is a very similar 

 species, but it is proportionally broader, more robust, and the dorsal valve more nearly cari- 

 nated, while the beak is not so much extended ; the striae are likewise stronger, and the ventral 

 valve is usually convex. This species attains to a larger size than O. elegantula ; though at the 

 time I first made the comparison in 1843, I had seen only specimens of about the same size. 



Fig. 3 a, h. The dorsal valves of young individuals. 



Fig. 3 c. The dorsal valve of a full grown individual, having the beak somewhat more extended 



than in other specimens, though by no means an unusual form. 

 Fig. 3 d. Ventral view of the same specimen. 

 Fig. 3 e. Profile view of the same specimen. 



Fig. 3 /. Cardinal view of the same, showing the elevation of the dorsal valve. 

 Fig. 3 g. Ventral view of a shorter specimen. 

 Fig. 3 h. Cardinal view of the same. 



Fig. 3 i. Cast of a dorsal valve of an elongated specimen. 

 Fig. 3 h. Cardinal view of the same. 



Fig. 3 /, m. The interior of the dorsal valves of a young and full grown individual. 

 Fig. 3 n. The interior of a ventral valve, showing th« muscular impression, lamella, etc. 

 Fig. 3 0. The same enlarged. 



