208 NEW YORK STATE MUSEUM 



Chonetes antiopa Billings 



Plate 45, figures 1-5; plate 46, figures 5 



Chonetes antiopa Billings. Palaeozoic Fossils. 1874. v. 2, pt i, p. 19 (not 

 figured) 



Original description. Shell small, semielliptical; cardinal angles about 90°; sides 

 nearly straight in the posterior third or half of the length, anterior angles uniformly 

 rounded; front margin broadly or gently convex; width about one fourth or one half 

 greater than the length. Ventral valve moderately and sometimes rather strongly convex, 

 most elevated about the mid-length; somewhat compressed at the angles; umbo usually 

 slightly elevated. Often the shell is more or less abruptly inflected about the mid-length, 

 with a flattened or only gently convex slope to the front margin. Sometimes there is a 

 shallow groove, which extends from the beak along the median line to the front. There 

 are two spines on each side of the beak, slightly sloping outwards, nearly erect, sometimes 

 gently curved, the convex side of the curve outwards. There may be a third spine at the 

 cardinal angle, but it has not yet been observed. 



The surface to the naked eye appears nearly smooth, but, when magnified, exhibits 

 about fifteen rounded, subangular striae in the width of one line. 



Width four or five lines. Although a large number of specimens have been collected, 

 none of them exhibit the area or the dorsal valve. 



To the above description should be added the fact that the median stria 

 of the ventral valve is usually more prominent than those adjoining while 

 one or two others may also be conspicuous. Except in its greater convexity 

 the species thus resembes the young of C. canadensis. The hinge line 

 in C. antiopa is without crenulations. 



While the characters of the species are well depicted in this description 

 it is clear that they are in many respects those ofCh. hudsonicus 

 Clarke. This agreement is seen in the outline, fine striation, shape of 

 spines, even the low median sinus on the ventral valve of the latter being 

 apparent in C h. antiopa. It is however a uniformly small shell never 

 attaining the size of Ch. hudsonicus. In describing other Chonetes of 

 this fauna we shall observe that the species of the Grande Greve limestones 

 and Gaspe sandstones present a series of forms which are in effect develop- 

 mental expressions of a single specific type. Within this series we shall find 

 embraced Ch. antiopa as the simplest term ; the relations of this to 

 Ch. hudsonicus are very close both in form and exterior. The next 

 stage is Ch. hudsonicus metatype gaspensis from which C h. 

 melonicus is distinguished chiefiy by its greater gibbosity and more 

 elongate hinge ; Ch. canadensis is in the same line of development so 

 far as its exterior is concerned but has reverted in the character of its hinge 

 to the nondenticulate type. 



Localities. Quite abundant at Perce Rock, from which the original 

 specimens were obtained. The specimens at Indian Cove and from the 

 lower beds on Dolbel's brook on the Forillon are less convex than those of 

 Perce but in other respects appear to be identical. 



