I/O NEW YORK STATE MUSEUM 



Camarotoechia dryope (Billings) 



Plaie 28, figure 2 



Rhynchonella dryope Billings. Palaeozoic Fossils. 1874. v. 2, pt i, p. 37, 



pi. 3A, fig. I, a-c 

 Camarotoechia dryope Clarke. N. Y. State Mus. Mem. 3. 1900. p. 41, 



pi. 5, fig. 20, 21 



Original description. Subcircular or subpentagonal; apical angle varying from about 

 95° in the smaller specimens to 130° in the larger. Slope on each side of the beak concave 

 or nearly straight for two or three lines, then slightly convex; sides rounded; front 

 margin, with a portion in the middle about equal to one third the width, either straight or 

 slightly concave. In the larger specimens the greatest width is about the mid-length; in 

 the smaller somewhat nearer the front. Width of a large specimen, thirteen lines; length, 

 eleven lines; depth of both valves near the front margin, eight lines. Ventral valve 

 varying from slightly to moderately convex; a portion on each side of the mesial sinus flat 

 or even slightly concave near the front margin; umbo narrow; beak incurved down to the 

 umbo of the dorsal valve. The mesial depression is rather less than one third of the 

 whole width, indenting the opposite valve, at the margin, to an extent equal to the depth 

 of both valves or nearly so. From the margin it becomes gradually more shallow with an 

 uniform curve until it becomes obsolete at about the mid-length of the shell, or a little 

 above; a rib on each side slightly longer than the others extends nearly to the beak, in 

 some specimens. There are three ribs only in the depression, in all the specimens 

 collected. The rib on each side presents a large flat, slightly convex or slightly concave 

 face, sloping upwards, and more or less inclined outwards from the bottom of the 

 depression. 



The dorsal valve is rather strongly convex. On a side view [fig. ib] the front margin 

 is nearly squarely truncated; the outline, from the most elevated point at the front, is 

 sometimes nearly straight for one third or one half the length, but in general it is gently 

 convex for that distance and then becomes more or less abruptly curved down to the beak 

 of the ventral valve. The umbo is of moderate size, rounded, abruptly elevated from the 

 beak in large specimens, sometimes with a very faint mesial depression for two or three 

 lines. The mesial fold is strongly elevated at the front margin but dies out at the mid- 

 length, or a little above. 



Surface with strong subangular ribs; four on the mesial fold and three in the mesial 

 depression. On each side of the mesial fold and depression there are usually five or six 

 ribs in the smaller and medium sized specimens, and seven, eight or nine in the larger. 

 The most common number is six on each side. 



The ribs are more strongly curved outwards towards their extremities than is repre- 

 sented in the above figures. 



Though we have observed the existence of this species in the Oriskany 

 of Columbia county, our collections at Gaspe show only a small shell that 

 can be regarded identical therewith. This is the more singular as it is not 

 regarded by Billings as a specially rare form. His specimens were collected 

 by Robert Bell at Grande Greve. 



