56 
PALEONTOLOGY OF NEW YORK. 
Devonian. In America, Amboccdia umbonata appears in the Corniferous lime¬ 
stone, and its existence is continued under more favorable conditions for devel¬ 
opment in the various faunas of the Hamilton group. In the latter faunas is 
also a larger form which has been described as A. pmumbona, Hall, and in the 
Chemung group A. umbonata var. gregaria, Hall, is a very abundant shell. The 
Orthis umbonata was identified in the Devonian of western France (Gahard) by 
Marie Rouault as early as 1851,* and has been redescribed and figured by 
(Ehlert in the work already cited. 
There also occurs in the Hamilton shales of western New York a species 
with spinous exterior (A. spinosa, sp. nov.) ; and in the final appearance of 
Amboc®lia in the Coal Measures, where it is represented by the Spirifer plano- 
convexus, Shumard, the same condition of exterior occurs. In the latter, how¬ 
ever, the surface spines are usually lost, the exterior appearing as in the 
Devonian species though showing the fine punctation or reticulation of the 
epidermal shell layer. 
Genus METAPLASIA, nov. gen. 
PLATE XXXIX. 
This name is proposed for the little shell described in 1859 as Spirifer pyxi- 
datus, Hall.f While it possesses a general spiriferoid aspect in outline, the 
structure of the hinge and deltidium, the pedicle-valve is the more convex and 
bears a broad fold, while the brachial valve is flat or slightly convex over the 
lateral extremities and depressed medially by a broad sinus. This reversal of 
the relative position of the fold and sinus is accompanied by some other 
peculiarities. 
The teeth are stout and unsupported by lamellae; the posterior extremities 
of the diductor impressions in the pedicle-valve are deeply impressed and sepa¬ 
rated by a short, thick septum. Anteriorly the muscular area is less clearly 
defined; from its distal margin diverge two ridges which were probably of 
vascular origin, and a few radiating furrows of similar character are seen on 
the lateral portions of the valve. 
*Bull. Soc. G6ol. de Fi-ance, 2nd ser., t. viii, 322. 
t Palseontology of New York, vol. iii, p. 428, pi. e, figs. 9-12. 
