50 Cincinnati Sociehj of Natvral History 



on the same plate, represent similar attempts to indicate the 

 outlines of the brachial valves of this species. They were 

 prepared from plaster casts, taken from specimens numbered 

 J. P. 4067 and 4024 respectively in the register of the Geolog- 

 ical Survey of Great Britain. These specimens were obtained 

 about 1 1 years ago at the same locality as that of the specimen 

 figured by Salter, namely Bird's-hill. All three specimens 

 show distinctly the strong convexity and the low, but com- 

 paratively broad median elevation demanded by Salter's 

 description and figures. Whether specimen J. P. 4078, repre- 

 sented by figure IE on plate II, belongs to the same species 

 of Hebertella is uncertain. Figures IF and IG probably give 

 the more usual outlines of the species. Figure IH represents 

 an unusually nasute specimen; the postero-lateral angles 

 undoubtedly are too angular. Figures 3e to 3h on plate III 

 indicate the amount of curvature, along the median line, of 

 the brachial valves bearing the same letters in figure 1 on plate 

 II, and figures 3E to 3H on plate III indicate the corresponding 

 lateral curvature across the center of the valves. 



These specimens of Hebertella from the Bird's-hill locality 

 apparently represent an unnamed species for which the term 

 Hebertella Llandiloensis here is proposed. From Orthis porcata, 

 M'Coy, if differs in its larger size and in the tendency toward 

 a distinct median elevation. Moreover, the beak of Orthis 

 porcata is not retrorse as in Orthis retrorsa, the former species 

 belonging to the Dinorthis snhquadrata group. Orthis grandis, 

 Sowerby (Murchison's Silurian System, 1839, p. 638, pi. 20, 

 figs. 12, 13), and Orthis grandis, Portlock (Report on the 

 geology of the County of Londonderry and of parts of Tyrone 

 and Fermanagh, Dublin, 1843, p. 452, pi. XXXII, fig. 25), are 

 two much more finely striated species, with a much more 

 quadrangular outline posteriorly, apparently belonging to the 

 Strophomenacea rather than to the Orthacea. 



All of the British specimens here figured were identified 

 by Dr. C. A. Matley, and were loaned by Dr. F. L. Kitchen, 

 the Paleontologist of the Geological Survey of Great Britain, 

 to Dr. F. A. Bather of the British Museum, for the preparation 



