EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 2O9 



Chonetes bilHngsi nov. 



Plate 41, figures 18-30 



Ch onetes laticosta (Hall) Billings, Palaeozoic Fossils. 1874. v. 2, pt i, p. 20 



Under Hall's name C h. laticosta Mr Billings described at some 

 length a small highly convex shell with few and strong ribs. This name 

 was introduced by Hall in 1857 [N. Y. State Cab. Nat, Hist. loth An. 

 Rep't, p. 119] for a Chonetes from the Onondaga limestone, but at a later 

 date the author withdrew the name identifying that shell with C h. 

 mucronatus of the Marcellus fauna [Pal. N. Y. 1867, 4: 124]. 



These Gaspe shells which are very abundant in various stages of 

 growth are characterized by the high gibbosity of the central region and 

 abrupt slopes to the margins in the pedicle valve and the coarse rounded 

 ribs separated by interspaces of about the same width. These ribs are 

 usually simple, extending from beak to margin and number from 16 or less 

 in small individuals to 26 in the largest shell seen. In full growth of the 

 shell the median rib becomes more pronounced than the rest on the anterior 

 margin and thus makes a low median angle at this margin. Extremely fine 

 concentric lines are visible under favorable preservation. The cardinal area 

 is narrow and only in rare instances are spines retained or developed at the 

 cardinal extremities. On the interior the brachial valve has a small erect 

 v-shaped cardinal process and short thin outer socket walls. On each of th<; 

 simple coarse ribs which correspond to the furrows of the exterior is a 

 single row of sharp pustules the median row being the most depressed, and 

 the two adjoining the most prominent. No trace of reniform or other 

 lateral depressions is evident. In all such small and coarse ribbed species 

 represented by C h. b i 1 1 i n g s i, C h. laticosta and C h. m u c r o n a t u s, 

 there is a natural similarity of expression extending even to the interior 

 characters of the brachial valve, but the distinctive differences of C h, 

 billingsi consist in its gibbosity, angulated front margin at maturity, 

 stronger, coarser and more uniformly simple ribs. In respect to these 

 characters in all the shells they are the most pronounced in that before us 

 and become progressively decreased in the upward range of the group, so 

 that it serves the purposes not only of paleontologic but also of geographic 

 distinction expressly to recognize this early manifestation of features 

 w^hich are less pronounced in C h. laticosta of the Onondaga limestone 

 and still further diminished in C h. mucronatus of the Marcellus and 

 Hamilton. 



Dwicnsions. A full sized example has a width on the hinge of 13 mm 

 and a length of 1 1 mm. From this the size ranges downward to a length 

 of 2 mm. 



Localities. Everywhere abundant in limestone 8 in the shore outcrops 



