ANIMALS. 181 



The species just named, and which has afforded the above diagnosis, agrees very 

 closely in its dentition with the so-called Cardita crenata of Goldfuss (vide ' Petrefacta,' 

 pi. 133, fig. 6), judging from a specimen in my cabinet collected at St. Kassian in the 

 Tyrol. I am consequently induced to regard the latter as belonging to the genus 

 under consideration. Neither species can be placed in Cardita ; as this genus has the 

 upper cardinal tooth of the right valve very much elongated posteriorly, so as to 

 occupy the entire space below the cartilage fulcrum ; and it is without any posterior 

 teeth : on the other hand, PleurojjJiorus has the corresponding cardinal tooth ordinarily 

 short ; and it possesses true posterior teeth : in both genera, it requires to be observed, 

 the cardinal dental /orw^^^/a is the same. Cypricardia might be adduced as an allied 

 genus, from its possessing posterior teeth ; but the receiving tooth is in the right valve, 

 and it has strong anterior teeth in addition : the same difference prevails in Pachyodon. 

 The recently formed genus Carditamera, typified with the Cardita affinis, agrees with 

 Pleurophorus in possessing similarly arranged posterior teeth ; but it has the upper 

 cardinal tooth of the right valve of the same elongated form as that of Cardita .■ it 

 also possesses anterior teeth. Coralliojjhaya — a genus which some might consider as 

 synonymous with Pleurophorus — differs in having a sinus in the pallial line. The genus 

 Myoconclia, placed by Mr. J. E. Gray in the present family,' may have a relation to 

 Pleurophorus : they differ, however, in their dental system ; since the former (which is 

 founded on the Oolitic M. crassa) is described by Mr. Sowerby, as having " an external 

 ligament, and one oblique elongated (cardinal) tooth in the left valve ; impressions of 

 the mantle not sinuated," and " no lateral teeth!'^" 



Pleurophorus costatus, Brown. Plate XV, figs. 13, 14, 15, 16, 17, 18, 19, 20. 



Arca costata. Brown. Trans. Manch. Geol. Soc, vol. i, p. 32, pi. vi, figs. 34, 35, 1841. 



— — ,, Brown's Fossil Concbology, pi. Ixxvii, figs. 31, 32, 1843 (?). 



— — „ Morris, Catalogue, p. 78, 1843. 



MoDioLA COSTATA, Brown. De Vernenil, Bull. Soc. Geol. de France, 2"° serie, t. i, p. 32, 



1844. 



— — „ Geol. Russ., vol. i, p. 224, 1845. 

 Cypricardia Murchisoni, Geinitz. Grundriss, p. 434, pi, xix, fig. 2, 1846. 



(?) MoDiOLA siMPLA, Keyserliny. Petschora-land, p. 260, pi. x; fig. 22, pi. xiv, fig. 1, 1846. 



— COSTATA, Brown. Tennant, Strat. List, p. 88, 1847. 

 Pleurophorus costatus, Brown. King, Catalogue, p. 11, 1848. 

 Myoconcha COSTATA „ Howse, Trans. T. N. F. C, vol. i, p. 245, 1848. 

 Cardita Murchisoni, Geinitz. Versteinerungen, p. 9, pi. iv, figs. 1-5, 1848. 



Diagnosis.. — " Shell transverse, oblong-ovate ; posterior (anterior, nobis) slope 

 exceedingly short ; anterior (posterior, nohis) slope very long ; umbones small, and 

 but slightly produced ; both valves provided with three prominent ribs, emanating 



^ Synopsis of the British Museum, p. 128, 1841. 

 ^ Mineral Conchology, vol. v, p. 103. 



