304 MISSISSIPPIAN BRACHIOPODA 



successively smaller towards the cardinal extremities. Internally a 

 strong median septum reaches from the beak to a point between one- 

 third and one-half the length of the valve, the dental plates diverge 

 anteriorly from the beak and reach anteriorly less than one-half the 

 length of the median septum. 



Brachial valve not known. 



Surface of the shell ornamented by rather strong, regular, sublamellose, 

 concentric markings, about three or four of which occupy the space of 

 one millimeter. 



Remarks. The species differs from its associate, S. missouriensis, in the 

 less strongly convex pedicle valve, in the nearly flat cardinal area with 

 its posteriorly sloping position, in the more obtuse beak of the pedicle 

 valve, and in the greater number of plications. 



Horizon. Glen Park limestone of the Kinderhook. 



DELTHYRIS NOVAMEXICANA (Miller) 

 Plate XXXVI, Figs. 15-24 



3881. Spwfera novamexicana, Miller, Jour. Cinn. Soc. Nat. Hist., vol. 4, 



p. 314, pi. 7, figs 10-10b. 

 1909. Spiriferina magnicostatus Weller, Bull. Geol. Soc. Am., vol. 20, 



p. 307, pi. 13, figs. 12-15. 



Description. Shell small, much broader than long, the greatest width 

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

 mucronate extensions. The dimensions of a somewhat imperfect and 

 distorted specimen, more than usually extended along the hinge-line, 

 are : length of pedicle valve -|-7 mm., length of brachial valve 6 mm., 

 width along hinge-line 24 mm., thickness 6 mm. 



Pedicle valve most prominent in the umbonal region, becoming com- 

 pressed towards the cardinal extremities; the mesial sinus of moderate 

 depth, rounded in the bottom, bounded laterally by a pair of strong, 

 rounded ribs which originate at the beak and which are prominently ele- 

 vated above the plications on either side; the beak rather small, pointed 

 and incurved; the cardinal area low, concave, with its lateral margins 

 sharply defined ; the delthyrium about as wide as high ; lateral slopes 

 convex from the cardinal to the anterior margins, the slope from the 

 umbo to the cardinal extremities concave, each one marked by three or 

 sometimes four clearly defined, rounded plications, beyond those which 

 bound the mesial sinus, they originate along the cardinal margin, and 

 decrease gradually in size towards the cardinal extremities, and on 

 shells greatly extended along the hinge-line one or more additional, 

 extremely faint plications may sometimes be detected; the largest of the 

 lateral plications are distinctly smaller than those which bound the 

 mesial sinus. Internally, the umbonal portion of the valve is solidified, 



