296 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXXIV, 
~PUGNAX WEEKSI, new species. 
Shell large, varying in shape from subtriangular or subovate to 
subpentagonal, and from elongate to transverse. As a rule highly 
gibbous, but sometimes of lower convexity, probably as a persistence 
of an immature character, young shells being usually discoidal. 
Ventral beak large, pointed, suberect, flattened, and spreading at the 
sides. Foramen apparently triangular and open. Dorsal beak 
rather inconspicuous, and strongly incurved. Fold and sinus very 
strong, usually broad and subquadrate, but sometimes narrow and 
sometimes rounded; typically divided by a medium sulcus so that 
it bears two plications, but occasionally the sulcus is so faint that the 
fold appears to be simple. Much more rarely three plications are 
found upon specimens referred to this species. There is always one 
‘rather distinct lateral plication on each side of the fold, with usually 
a second, which is also sometimes distinct but may be obscure. All 
the plications are confined to the marginal portions of the shell, and 
they vary in different specimens not only as to distinctness but also 
as to being angular or rounded. In young specimens the shell is 
broadly oval and discoidal. The fold develops first, and later its 
median sulcus and the lateral plications. 
Upon the interior the ventral valve is provided with dental 
lamellz and the dorsal valve apparently with strongly diverging 
socket plates connecting with a hinge plate, which is also joined to 
a fairly long, high, median septum. 
The posterior portion, especially of the ventral valve, is rather 
thick shelled, and moderately strong though not well-defined muscular 
imprints are retained in many instances. 
In general appearance certain variants of this form are very sug- 
gestive of some species of Athyroids, as, for instance, Composita 
trinuclea, but more especially the forms grouped by Abich under the 
title Spirigera protea, some of which, unlike (. trinuclea, have lateral 
plications. Aside, however, from the fact that these shells appear to 
be without spiralea, the configuration of the beak of the ventral 
valve indicates almost to a certainty that we have not to do here with 
an Athyroid. In fact, there can be but little doubt that this form is 
one of the Rhynchonellide. I have, however, been in some doubt as 
to what genus it would best be cited under. The choice seems to lie 
between Rhynchonella s. s. and Pugnax. The type species of Rhyn- 
chonella and Pugnax are very similar in external form, but Rhyn- 
chonella loxia has a septum in the dorsal valve, while Pugnax pugnus 
is without that structure. In general appearance, therefore, 72. weehsi 
* Geologische Forschungen in den Kaukasischen Liindern, 1 Theil, Hine Berg- 
kalkfaune aus der Araxesenge bei Djoulfa in Armenien, Wien, 1878, p. 52 et seq. 
