462 MISSISSIPPIAN BRACHIOPODA 



edge of the internal characters, which in this case can only be gained by 

 sectioning the specimens, the true relationships of the species cannot be 

 certainly determined. So far as can be determined, considering both the 

 external form and the internal structures, the species seems to be most 

 closely allied to the meristoid genus Camarophorella, where it is here placed, 

 but further knowledge of the shells may show that the species should be 

 considered as the type of a new genus. The external feature of the shell 

 which seems to be especially characteristic, is the presence of a faint 

 median sinus of the brachial valve which does not continue to the front 

 margin in mature examples. The general outline of the shell seems to be 

 rather variable, judging from the three examples studied. Of the pre- 

 viously known species of Camarophorella this species most closely re- 

 sembles C. mutabilis Hyde. 1 The general contour of the two species is essen- 

 tially the same, including the faint median sinus in the posterior portion 

 of the brachial valve, but C. missouriensis differs from C. mutabilis in the 

 entire absence of the faint radiating stria? of that species. 

 Horizon. Louisiana limestone. 



Genus ROW LEY ELL A Weller 



Description. Shells small, subovate in outline, with subequally convex 

 valves, fold and sinus wanting, the surface of the shell marked only by 

 inconspicuous concentric lines of growth. Pedicle valve with the beak 

 moderately incurved and perforated at its apex by a subcircular foramen 

 which encroaches wholly upon the umbonal region, in contact with the 

 delthyrium only at its apex, the delthyrium closed by deltidial plates. 

 Internally a strong median septum is present which reaches about one- 

 third the length of the valve, it supports a spondylium formed by the 

 union of the dental plates. In the brachial valve is a strong median sep- 

 tum which reaches anteriorly for one-third or more of the length of the 

 valve, its connection with the hinge-plate and brachidium has not been 

 determined and if a platform beneath the hinge-plate, such as occurs in 

 Camarophorella is present, its outer margins do not join the inner surface 

 of the valve to form the pair of finger-like cavities which are present in 

 that genus; the attachment of the brachidium to the crura and the form 

 of the jugum unknown, the spiral cones are directed laterally and consist 

 of about four volutions. 



Rema-rks. The terebratuliform contour of the shell of the single mem- 

 ber of this genus, strongly suggests its being a loop-bearing brachiopod, 

 and the genotype was originally described as a Terebratula. At the time 

 the generic name Rowleyella was proposed for this species the presence of 

 a spiral brachidium had not been detected, and while it was recognized 

 that the presence of a median septum in the pedicle valve was an un- 



iProc. Boston Soc. Nat. Hist, vol. 34, No. 3, p. 56 (1908). 



