ORTHIDtE. 251 



the mistaken denomination of Orthis grandis, Murchison, to which species the shell 

 in question does not belong. In 1845 Mr. Salter applied to it the catalogue name of 

 0. injlata. In 1846 it was described and imperfectly illustrated by M'Coy at p. 32 of 

 his ' Synopsis of the Silurian Fossils of Ireland.' In 1848 Mr. Salter gave a full descrip- 

 tion of his 0. injlata and var. retrorsa. In 1852 Prof. M'Coy claimed priority for his name 

 porcata ; and this claim was subsequently (in 1859 and 1866) conceded by Mr. Salter, 

 and adopted by the generality of British and foreign palaeontologists. In America, 

 however, in 1860 it received the designation of 0. Carleyi from Prof. Hall, and that 

 of Anticostiensis from Mr. Shaler. Some British palaeontologists have also proposed to 

 add 0. occidentalis. Hall, 0. sinuata. Hall, 0. suhquadrata. Hall, 0. suhjugata, Hall,i and 

 0. formosa, to the synonyms of 0. porcata. While I concur with Messrs. Sharpe 

 and Salter that several of the above-named American fossils may be varieties of a single 

 variable species, I am still very doubtful if they can with certainty be placed among 

 the synonyms of the species under description. At p. 72 of the '12th Annual 

 Report of the Regents of the University of the State of New York,' published in 

 in 1859, I find the following statement by Prof. J. Hall: — " 0. occidentalis, with 

 0. sinuata and 0. suhjugata, may form but a single species, though, from the collections 

 in my hands in 1847, I found what appeared to be a satisfactory means of distinguishing 

 them. Since examining the species of the Lower Helderberg Limestone, I have found 

 numerous forms which appear as closely allied as do these, but which are nevertheless 

 clearly distinguished by their interior markings. I am not satisfied that the European 

 species, Orthis porcata, is identical with ours." At p. 223 of his work on ' British 

 Palaeozoic Possils,' M'Coy also intimates that 0. occidentalis and 0. sinuata are closely alUed 

 forms, but probably distinguished from 0. porcata by the greater comparative depth of the 

 ventral valve and its deep mesial sinus, which abruptly indents the margin. There seems 

 to be also a difference in the ribbing. 0. porcata varies, like all its congeners ; and in 

 PI. XXXI I have endeavoured to illustrate some of its more prominent modifications in 

 shape, the ribs being sometimes more immerously interpolated in some examples than in 

 others. In England and in Ireland the species exists in great abundance under the con- 

 dition of internal and external casts, but is very rarely found with its shell well preserved, 

 or with its two valves united. In the Island of Anticosti, however, perfect examples of 

 this species are common, and seem very constant in their shape and character, these last 

 having been correctly described and illustrated by Mr. Billings at p. 135 of the first 

 volume of the ' Memoirs of the Geological Survey of Canada (Palaeontological Series).' 



Position and Locality. In the British Isles Orthis porcata seems to be restricted 

 to the Caradoc formation, of which it . is a characteristic fossil. In England it occurs 

 all through Shropshire ; Mr. Salter mentions its occurrence at Bettws-y-coed, Caernarvon- 



^ Full descriptions and figures of these species will be found in vol. i of the ' Palseontology of New 

 York,' p. 127, &c. 1847. 



