PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 303 
ORTHAMBONITES EUCHARIS (Ulrich and Cooper) 
Orthis eucharis UtricH and Cooper, Geol. Soc. Amer. Special Pap. 13, p. 99, pl. 14, E, 
figs. 15-18; pl. 57, B, figs. 10-12, 14-16, 1938. 
Types.—Lectotype: 95875c ; paratypes : 95875a,b,d-h. 
Horizon and locality—Upper Pogonip group (mottled zone 700 feet below 
the Eureka quartzite) in Nevada: Ridge east of Frenchman Flat, Las Vegas 
(1°) Quadrangle. 
ORTHAMBONITES ? EXFOLIATUS (Raymond) 
Hebertella exfoliata RAyMonp, Amer. Journ. Sci., ser. 4, vol. 20, p. 370, 1905. 
Plectorthis exfoliata (Raymond), Ann. Carnegie Mus., vol. 7, No. 2, p. 238, pl. 35, figs. 11, 
12, IQII. 
Orthis costalis HAut, Pal. New York, vol. 1, pl. 4, bis, fig. 4b, 1847. 
The description and figures of this small orthid have never permitted accurate 
understanding of the species, and this is true of the specimens available to the 
writer. The specific name is aptly chosen because all the specimens available 
have been broken from a somewhat dirty limestone and are much exfoliated, thus 
not permitting an understanding of the true nature of the exterior. The interior 
hitherto has never been described, except for the pedicle muscles. 
A few specimens in sandy or silty matrix were subjected to treatment by acid 
and the shell dissolved away from the matrix. The pedicle valves reveal strong 
dental plates and a somewhat elongate muscle field having prominent diductor 
scars. 
The brachial valve cardinalia consist of a prominent but low notothyrial plat- 
form having a prominent cardinal process thickened anteriorly. Brachiophores 
are short and thick. It is difficult to tell, from the specimens available, if plates 
support the brachiophores and are recumbent on the floor of the valve or if the 
notothyrial platform is that common to the Orthidae. The structures lie too 
close to the valve floor to be assigned to Plectorthis. The writer therefore tenta- 
tively assigns the species to Orthambonites even though the interior is atypical 
and the exterior suggests Desmorthis. 
Horizon and locality—Day Point formation, vicinity of Chazy, Rouses Point 
(15’) Quadrangle; 3 miles north of Plattsburg and Valcour Island, Plattsburg 
(15’) Quadrangle. 
ORTHAMBONITES FRIENDSVILLENSIS Cooper, new species 
Plate 36, A, figures 1-8 
Shell of medium size for the genus, strongly inequivalved, the pedicle valve 
having the greater depth. Outline subquadrate; length and width nearly equal. 
Lateral margins straight or slightly concave; anterior margin broadly rounded. 
Cardinal extremities a right angle. Anterior commissure rectimarginate to sul- 
cate. Surface marked by narrow, rounded costae separated by spaces narrower 
than the costae. Costae ranging in number from 32 to 36, and with from 6 to 8 
occupying a space of 5 mm. at the front. 
