266 
PALEONTOLOGY OF NEW YORK. 
The latter genus was established in the same year (1859) as Renssel^ria, 
and was founded upon a small plano-convex species with smooth exterior, the 
Rhynchonella glans-fagea, Hall, from the Upper Helderberg group. 
The original description and figures illustrative of this genus did not give the 
structure of the brachidium with accuracy, but this was afterwards made out 
by Dr. Carl Rominger and shown in his excellent figure, given in the Sixteenth 
Report on the New York State Cabinet of Natural History (p. 47, 1863), and 
which is reproduced in this place. Subsequent examinations have endorsed the 
correctness of Rominger’s determination and also show that the type upon which 
it is constructed is the same as in Renssel^eria ; the actual differences of 
expression appearing (1) in the shortness of the jugal processes, (2) in the less 
extended anterior plate, and (3) in the prominent median crest or ridge upon 
that plate, not produced posteriorly into a rod-like apophysis. 
It has already been observed that in the early (Lower Helderberg) species of 
RENSSELiERiA, sucli as R. mutabiUs, some of these features, as the length of the 
crura, and the development of the median process are not so advanced as in 
the later and typical species of the genus, nor as in R. {Beachia) Suessana. 
Upon farther examination of more extensive material it is found that this 
type of brachidium-structure has, without essential variation in itself, been 
associated in Devonian faunas with a considerable variety of external form and 
ornamentation of the shell. This fact has already been observed by some 
authors. Reference has been made to QUhlert’s observation* of a similar 
brachidium, with a perforated hinge-plate, in certain small plano-convex or 
biconvex plicated or ribbed species, Terebratula Guerangeri, Centronella Bergeroni 
and C. Gaudryi, from the Devonian of western France, all of which he has 
referred to Centronella on the basis of this structure. Derby has found a 
brachidium of similar structure, though somewhat more nearly approaching 
that of Renssel^ria, in another small and strongly ribbed biconvex species 
from the Devonian of the State of Matto Grosso, Brazil, described by him 
under the name Centronella ? Margarida.-f 
* Bull, de la Soc. d’Etudes Scientif. d’Angers, 1883, pp. 1-11, pi. i, figs. 1-11; pi. ii, figs. 1-6 ; ditto, 
1885, pp. 1-5, plate, figs. 1-19. 
t Not^ sobre a Geologia e Paleontologia de Matto Grosso : Archivos do Museu Nacional do Rio de Jan¬ 
eiro, vol. iv, p. 84, figures. 1890. 
