192 NEW YORK STATE MUSEUM 



Genus rhynchotreta Hall 

 [Ety.: puyxo?, beak; rprjrd, with a hole] 



(1879. ^- ^- ^^^^^ ^'"''^- "'^^- ^^^^^- ^^^^^ '^"- ^'(^P'^, P- 166; 1893. 

 Pal. N. Y. V. 8, pt 2, p. 185) 



Shell triangular; surface with angular plications. Beak of pedicle 

 valve straight, produced beyond that of the opposite valve^ extremity 

 perforate, the foramen with an elevated margin. Two longitudinally 

 striated deltidial plates fill the delthyrium. Teeth slender, curving, 

 proceeding from a broad curving hinge plate in the pedicle valve. 

 Brachidium a slightly modified loop. 



Rhynchotreta cuneata var. americana Hall (Fig. 105). 

 Atrypa cuneata Hall (1852. Pal N. Y. 2:276, pi. 57, 



fig. 4a-r) 



Distinguishing characters. Triangu- 

 lar and cuneiform outline; longer 

 than wide; elongate angular beak 

 of pedicle valve with compressed, 

 flat or concave sides; wide, deep sinus 

 in adult, extending two thirds to the 

 beak; profound frontal emargination; 

 strong angular plications, three in 



Fig. 105 Rhynchotreta cuneata var. 



americana siuus, four ou fold, the two Central ones 



most prominent; numerous regular, fine thread-like concentric 

 striae; minutely papillose surface. 



Found in the Clinton lenses and the lower Rochester shale and 

 particularly in the Bryozoa beds, where it is abundant; rarely above 

 thiso Niagara sections. Also at Lockport and elsewhere (Hall). 



Genus camarotoechia Hall & Clarke 



[Ety.: xaijApa, arched chamber; rolxo?, partition] 



(1893. Pal. N. Y. V. 8, pt 2, p. 189) 



Shell rhynchonelloid, trihedral in contour, with shallow pedicle 

 and convex brachial valve; no hinge area; beak of pedicle valve 

 projecting and incurved. Surface radially plicate, sinus and fold in 

 pedicle and brachial valves respectively. Distinctive internal char- 

 acters (separating this genus from other " Rhynchonellas ") are: a 



