224 
PALEONTOLOGY OF NEW YORK. 
ANASTROPHIA, Hall. 1867. 
PLATE LXIII. 
Under the term Anastrophia has been grouped a number of species with 
reversed convexity, the disparity of the two valves in this respect surpassing 
that prevailing in Parastrophia. Their external surface is covered with 
numerous tine and sharj) dichotomizing ribs, extending to the apices of the 
beaks and frequently crossed by delicate concentric lines. The type of this 
genus is the Pentamerus Verneuili, Hall, of the Lower Helderberg shaly lime¬ 
stone, and with it are to be associated the Atrypa interplicata, (Sowerby) Hall, 
and Anastrophia internascens, Hall, of the Niagara group; the Terebratula dejiexa, 
Sowerby, of the Wenlock limestone, and the shell passing under the same name 
in a corresponding fauna of the Island of Gotland. 
In this group again, the internal apophyses are subject to some variation. 
The spondylia of the valves are quite large, extending not less than one-third 
the length of the shell. As in Parastrophia, that of the pedicle-valve is the 
wider and is supported by a median septum near its anterior extremity. In 
the earlier species, A. internascens, A. dejiexa, this spondylium may be thus sup¬ 
ported for nearly or quite its entire length, but in A. Verneuili, the latest repre¬ 
sentative of the group, the structure is usually the same as in later members of 
Parastrophia. On Plate LXIII is given a figure of an interior of this species 
in which the lateral walls of the spondylium have folded, one over the other, 
and thus formed a tubular cavity open at both ends. What the significance of 
this modification may be, can not be judged from the single specimen. In the 
brachial valve the convergent plates generally rest upon the inner surface of 
the shell, though at times, in A. Verneuili, the spondylium is supported at its 
anterior extremity. The crural plates are extravagantly developed, forming 
two broad wing-shaped vertical expansions, concave on their outer surfaces; 
their upper edges are curved over the hinge-line, their anterior edges broadly 
notched, and below this point appears the base of attachment for the crura; 
the walls of the spondylium being connected with them at the most convex 
point of their inner surfaces. The dental sockets are always small, and old 
shells frequently show a fiilse foramen in the beak, which is simply an exten- 
