48 Cincinnati Society of Natural History 



This figure appears to be based upon specimen 11212 in the 

 Museum of Practical Geology, in London, and two additional 

 figures of this specimen, one from a plaster cast (Fig. lx\), 

 the other from a dental wax squeeze (Fig. IB) are presented 

 on plate II. A second specimen, collected at the type locality 

 about 11 years ago, consists of two small slabs, one the obverse 

 of the other, bearing the numbers J. P. 4031 and 4032, in the 

 Museum of the Geological Survey of Great Britain, Fig. IC 

 on plate II is based on a plaster cast of a part of the slab num- 

 bered 4032. The type locality is described as: the Old Quarry 

 (the first quarry south of the Quarry Cottage) 200 yards north- 

 west of Birdshill farm, Llandeilo, 6" 33 S. W. E., 1" 212 Car- 

 marthen, in southern Wales. Horizon: Bala. 



It is evident that Salter's description of Orthis ret'rorsa 

 was intended to contrast with that of his Orthis inflate, printed 

 on page 372 of the same publication, in which the brachial 

 valve is described as "strongly gibbous, a little emarginate in 

 front," while the pedicel valve is described as "convex at the 

 beak, then flat, or broadly depressed along the middle, the 

 sides recurved; its area broadish, at right angles to the valve." 



Orthis inflata was described from the Coniston limestone, 

 in Westmoreland, in northern England; and was stated to 

 occur also in North Wales. One of the specimens in the collec- 

 tions of the Geological Survey of Great Britain numbered 

 26039, and listed as ''Orthis, Coniston limestone, Coniston," 

 represents a pedicel valve of this species. The small fragment 

 of the hinge area remaining on each side of the foramen is 

 distinctly at right angles to the valve, and the quadrangular 

 muscular impression follows the description presented by 

 Salter. This specimen is illustrated by figure ID, on plate II. 

 Evidently Orthis inflata belongs to the Dinorthis subquadrata 

 group of species, while Orthis retrorsa is a retrorse form, closely 

 similar to, if not identical with, Dinorthis carleyi among 

 American species. 



The Coniston limestone is a member of the Bala group; 

 therefore both Orthis inflata and Orthis retrorsa belong to the 

 same general group of strata, but one species may have pre- 



1 



