280 
PALEONTOLOGY OF NEW YORK. 
is divided by three or four parallel finer vessels, which are given off from the 
margin of the trunk-sinus at right angles. In the larger valve on the inner 
side of the outer pair of trunk-sinuses, may be seen fine branches, originating 
at sharp angles. Further, in this valve may sometimes be seen, between the 
outer and inner, and also between the two inner trunk-sinuses, two finer radi¬ 
ating veins. All these vascular sinuses appear to unite in this valve to form a 
large lacune surrounding the area of muscular insertion. A ridge-like, elongate 
callosity crossed by irregular furrows, follows the cardinal margin on the dorsal 
valve.” 
Type, Terebratula Archiaci, de Verneuil. 
Observations. Leaving out of consideration for the present the peculiar 
structure of the brachidium, we find the other characters of the shell suffici¬ 
ently distinct from those of Renssel^ria and its allies; and these differential 
features are found in the general smoothness of the exterior,"^ the inflexion 
of the cardinal and lateral margins of the valves, the prominence and sharp 
delimitation of the diductor scars of the pedicle-valve, and the subcylindrical 
elevation of the hinge-plate into a veritable cardinal process, in which all traces 
of supporting lamellae are lost, and whose posterior face is grooved and striated 
by the insertion of the muscles. This latter feature is unusual in the palaeozoic 
terebratuloids, and is at once suggestive of the structure in the large and heavy 
rhynchonelloids (Plethorhynchus), so that it proves a distinctive character of 
importance. 
An excellent representative of this type of structure is the American Oris- 
kany species, originally described f as Meganteris ovalis, Hall, but which has 
been subsequently and currently referred to RENSSELiERiA. In the original 
description the similarity of the internal casts to those of Megalanteris Archiaci 
was noted. Megalanteris ovalis is not an abundant species in the Oriskany 
sandstone of New York and Ontario, and is represented in the formations in 
the vicinity of Jonesboro, Illinois, by a smaller, more elongate form with erect 
beak, deep cardinal and marginal excavations, the Rensselceria Condnni, of 
* Internal casts frequently show a minutely radiate surface about the inarg-ins, but this structure prob¬ 
ably belongs to the inner laminjE of the shell. 
t Tenth Annual Report on the Condition of the N. Y. State Cabinet of Natural History, p. 101. 1857. 
