Forty-fifth Report on the State Museum. 



Schizophoria, King. 1850. 



XII. Group of Orthis resupinata. Martin. 



(Plate 11, Figs. 18-23.) 



Shells resupinate or with normal convexity reversed as in 

 Groups IV, Y, YI. Surface very finely striate, the stria? being 

 hollow, tubulose and produced into short spines as in Rhipidomell a. 



In the pedicle-valve there is a short subquadrate or obcordate 

 muscular area with thickened, elevated margins, and deeply sunk in 

 the substance of the shell ; in the opposite valve a less distinctly 

 defined, quadripartite area. In the brachial valve the crural 

 plates are erect and divergent ; the cardinal process, which in 

 young shells, has much the same character as in Rbipidomella, 

 becomes resorbed and thus narrowed with age, making a thin 

 and sharp ridge ; concomitant with this change is the formation, 

 in the delthyrial cavity, of one, two or even three minor ridges 

 on each side of the original process, so that in old shells the pos- 

 terior face of the process appears to be multilobate. In this 

 valve four (rarely six) deep pallial sinuses take their origin 

 at the anterior margin of the muscular area, passing forward as 

 broad, simple, subparallel bands, to near the margin of the valve, 

 where they bifurcate and become arborescent. Shell substance 

 highly punctate. 



(Upper Silurian— Coal Measures.) 



Orthotichia, Hall. 1892. 

 XIII. Group of Orthis ? Morgan ian a, Derby. 

 (Plate 12, Figs. 14-17.) 

 External form as in Schizophoria. In the pedicle-valve the 

 dental lamellae are highly developed, between them lying a 

 conspicuous median septum ; muscular area not deeply impressed. 

 Shell substance punctate. 



(Carboniferous ; Brazil, India.) 



Enteletes, Fischer de Waldheim. 1830. ■ 



XI Y. Group of Enteletes Zamarcki, Fischer de Waldheim. 



(elate 12, Figs. 18-21.) 



Valves strongly inflated; brachial valve the more convex. 



Surface coarsely ribbed and covered with fine radial stria*. 



Hinge-line short; cardinal area of pedicle valve highly 



140 



