294 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Genus ORTHAMBONITES Pander, 1830 
Orthambonites PANveER, Beitr. Geogn. Russ. Reiches, p. 80, 1830. 
This name has long been under the synonymy of Orthis but was lately revived 
by Cooper (1942) for the biconvex orthids. The genus Orthis as restricted is a 
concavo-convex shell having some similarities to Cyrtonotella. On the North 
American continent a few species only conform to the generic definition of re- 
stricted Orthis ; consequently, the need of a name for the host of biconvex forms 
becomes apparent. 
The species placed under Orthambonites in this monograph are actually a com- 
posite lot. Some of them conform closely to the description of the genus, but 
others obviously are more remotely connected to it. Many more species will have 
to be described and considerable work performed on the internal characters of a 
host of species now indifferently referred to Orthis before the true generic affini- 
ties of Orthambonites and its derivatives will have been made known. 
As used here the genus Orthambonites is for biconvex orthids having a costate 
ornamentation and with orthoid cardinalia and the pedicle musculature of the 
Orthidae. A few of the species referred here do not conform strictly to this type, 
such as O. bifurcatus, O. brachiophorus with its unusually long brachiophores, 
O. dinorthoides with its elongate pedicle muscle field, and O. subconvexus. 
ORTHAMBONITES ACUTIPLICATUS (Raymond) 
Plate 33, C, figures 8-11 
Orthis acutiplicata RAYMOND, Amer. Journ. Sci., 4th ser., vol. 20, p. 370, 1905; Ann. Carnegie 
Mus., vol. 7, No. 2, p. 237, pl. 35, figs. 8-10, 1911. 
Types.—Lectotype: Carnegie Mus. 5458; paratypes: Carnegie Mus. 5459, 
5460. 
Horizon and locality—Day Point ? formation in New York: Southern end of 
Valcour Island, Lake Champlain, Plattsburg (15’) Quadrangle. 
ORTHAMBONITES ANGULATUS Cooper, new species 
Plate 36, C, figures 19, 20 
Shell large for the genus, known only from the pedicle valve ; wider than long ; 
hinge forming the widest part ; cardinal extremities produced into small, acutely 
angular ears ; sides gently rounded ; anterior margin fairly strongly rounded ; sur- 
face costate, costae 17 in number, angular. 
Pedicle valve moderately convex in lateral profile with the greatest convexity 
in the median region ; anterior profile broadly convex, the median region some- 
what narrowly rounded but the lateral slopes long and gentle; umbonal region 
slightly swollen, the swelling continued to the anterior margin as a low but in- 
distinct fold. Interarea moderately long, slightly curved, approximately ortho- 
cline. Teeth small, delthyrial cavity deep; dental plates short ; umbonal cavities 
mostly filled; muscle field with a short thickening anterior to its front margin; 
diductor scars slender; adductor track wide. 
