DESCRIPTION OF SPECIES BRACHIOPODA 307 



line a little shorter than the greatest width of the shell and the cardinal 

 extremities a little ronnded. Pedicle valve very prominent in the umbo- 

 nal region, the beak rather blunt and somewhat incurved; mesial sinus 

 originating at the beak, rounded in the bottom, becoming broad and deep 

 anteriorly and in large individuals being much produced in a lingual 

 extension, not sharply defined laterally ; lateral slopes of the valve usually 

 convex throughout, but sometimes becoming a little concave toward the 

 cardinal extremities; cardinal area concave, becoming strongly so in 

 large individuals ; internally the dental plates are strongly developed and 

 extend well toward the front of the shell ; they are conspicuously bilamel- 

 late and cleave readily along their median plane; posteriorly a trans- 

 verse plate connects the dental lamellas, its direction being nearly parallel 

 with the cardinal area, but somewhat depressed below the surface of the 

 area. Brachial valve about equally convex with the pedicle, most prom- 

 inent at about its middle point ; median fold rounded, becoming strongly 

 elevated toward the front; lateral slopes convex throughout or becoming 

 a little concave toward the cardinal extremities. Surface of the shell 

 marked by rather broad, flattened, simple plications upon the lateral 

 slopes, there being fifteen to twenty upon each side of the fold and sinus 

 on each valve; these plications are progressively smaller toward the car- 

 dinal extremities, the last five or more becoming very obscure; the fold 

 and sinus are non-plicate; surface of both valves also marked by concen- 

 tric lines of growth which are more or less irregularly developed. 



The dimensions of two individuals from the Burlington limestone are : 

 Length, 67 millimeters and 50.5 millimeters ; width, 81 millimeters and 

 73 millimeters ; length of hinge line, 73 millimeters and 62 millimeters ; 

 thickness, 60 millimeters and 41 millimeters. 



Remarks. — Spirifer planus is typically a member of the Burlington 

 limestone fauna, and the above description has been made from examples 

 occurring in that formation. In the Fern Glen formation a single 

 example has been observed which is merely a fragment of the umbonal 

 region of the pedicle valve, showing both the internal and the external 

 surfaces. Interiorly this fragment clearly shows the strong dental plates 

 which are so characteristic of the species and which are so unlike the 

 similar parts of any other associated Spirifer. 



SPIRIFERINA MAGNICOSTATUS n. sp. 



Plate 13, figures 12-15 



Description. — Shell small, broader than long, with the greatest width 

 along the hinge line, the cardinal extremities often produced into mucro- 



