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,’ 
pl. 133, fig. 6), judging from a specimen in my cabinet collected at St. Kassian in the 
Tyrol. Iam consequently induced to regard the latter as belonging to the genus 
under consideration. Neither species can be placed in Cardifa ; 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, Plewrophorus has the corresponding cardinal tooth ordinarily 
short ; and it possesses true posterior teeth : in both genera, it requires to be observed, 
the cardinal dental formula 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 affnis, 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. Coralliophaga—a genus which some might consider as 
synonymous with Plewrophorus—differs in having a sinus in the pallial lime. The genus 
Myoconcha, placed by Mr. J. KE. 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 JZ. crassa) is described by Mr. Sowerby, as having “an external 
ligament, and ove oblique elongated (cardinal) tooth in the left valve; impressions of 
the mantle not sinuated,” and “xo Jateral teeth.” 
PLEUROPHORUS COSTATUS, Brown. Plate XV, figs. 13, 14, 15, 16, 17, 18, 19, 20. 
Axca costata, Brown. Trans. Manch. Geol. Soc., vol. 1, p. 32, pl. vi, figs. 34, 35, 1841. 
— — WA Brown’s Fossil Conchology, pl. Ixxvil, figs. 31, 32, 1843 (7). 
— “ ue Morris, Catalogue, p. 78, 1843. 
Moproxa costata, Brown. De Verneuil, Bull. Soc. Géol. de France, 2™° série, t.i, p. 32, 
1844. 
= — a Geol. Russ., vol. i, p. 224, 1845. 
CypricARDIA Murcuisoni, Genitz. Grundriss, p. 434, pl. xix, fig. 2, 1846. 
(?) Mopioxa simpia, Keyserling. Petschora-land, p. 260, pl. x, fig. 22, pl. xiv, fig. 1, 1846. 
— cosTaTa, Brown. Tennant, Strat. List, p. 88, 1847. 
PLEUROPHORUSs cosTaTUs, Brown. King, Catalogue, p. 11, 1848. 
Myoconcna costata Be Howse, Trans. T. N. F. C., vol. i, p. 245, 1848. 
Caxpita MurcuHisont, Geinitz. Versteinerungen, p. 9, pl. iv, figs. 1-5, 1848. 
Diagnosis..—“ Shell transverse, oblong-ovate; posterior (anterior, 70d7s) slope 
exceedingly short; anterior (posterior, zodis) slope very long; umbones small, and 
but slightly produced; both valves provided with three prominent ribs, emanating 
I Synopsis of the British Museum, p. 128, 1841. 
2 Mineral Conchology, vol. vy, p. 103. 
