BRACHIOPODA. 159 



It ought, perhaps, to be observed that in a postscript note circuhited with 

 some copies of the Twelfth Report on the New York State Museum of Natural 

 History, the name Orthonom^a was proposed as a generic designation for 

 Orthis ? erratica. Should it become desirable to distinguish these finely striated 

 species from the more typical coarsely plicated Zygospira and the biconvex 

 Catazyga, this term would be entitled to consideration. 



Genus CLINTONELLA. gen. nov. 



PLATE Lll. 



Diagnosis. Shells usually small, suboval in outline ; valves subequally 

 biconvex, the axis of greatest convexity being oblique, making an angle of 

 about 55° with the vertical axis of the shell. Pedicle-valve with a small 

 umbo, which is compressed laterally, the apex being slightly incurved. The 

 cardinal area is replaced by a wide triangular delthyrium, which is unaccom- 

 panied by any trace of deltidial plates. The medially elevated umbo merges 

 anteriorly into a sinus which makes a deep flexure at the margin ; it bears two 

 plications, both of which reach the beak ; sometimes a trace of a third plication 

 may be seen. The lateral slopes bear from four to eight radial plications of 

 smaller size. 



On the interior the teeth are prominent, strongly recurved at their tips and 

 supported by lamellaB which terminate abruptly. The lower and inner mar- 

 gins of these lamellse are thickened, contracting the pedicle cavity, which is, 

 consequently, narrow and deep. The diductor scars are of moderate size, 

 tiabellate in outline and deeply impressed at their posterior extremity. They 



Anticostiensis and horealis "are only variations in shape of the same species, but specifically distinct 

 from the Zygospira (Athyris ?) Headi of Billings." Further, in indicatin<f the differences between A. Headi 

 and A. Anticostimsis, he says : " the most marked external characters consist in Headihaying in the dorsal 

 valve a somewhat deep longitudinal depression or sinus, while, on the contrary, Anticostiensis has the sinus 

 on the ve'itral valve." On the preceding page, in treating of Z. erratica, the author says : •' Z. erratica also 

 bears some resemblance to Z. Headi in its external form, especially as in both species there is a somewhat 

 deep sinus in the dorsal valve." It seems probable from these statements that Mr. Davidso.v has confounded 

 the typical A. Headi with the variety A. Anticostiensis, and this supposition is apparently borne out by the 

 assertion that the Rev. Mr. Glass succeeded in developing the brachial apparatus in Z. erratica. This 

 species, as far as we know, is invariably preserved as sandstone casts or in a matrix of sandstone, and to 

 develop its internal apparatus has proven an impossibility. The specimens of Z. Anticostimsis are, how- 

 ever, usually in limestone, and are very favorable subjects for such treatment. 



