NATURAL SCIENCES OP PHILADELPHIA. 11 



= }fac(ra ovata, McCoy,) a common species from the yellow sandstones of Bur- 

 lington. This species Messrs. Meek and Worthen supposed to be congeneric 

 with their Cardiopsis radiaia, (Proc. Acad. Nat. Sci. Phil., June, 1861, p. 144). 

 From the same beds, Mr. C. A. White has more recently described a similar 

 species under the name of Cardiomorpha {Cardiopsis?) parvirostris, (Proc. Bos. 

 Soc. Nat. Hist., Jan., 1862, p. 31), which has the small beak and Luciniform as- 

 pect of several other species referred by authors to the same genus * It was 

 some time since remarked, however, by Mr. White, that amongst all his speci- 

 mens of these two species, the left valves of C. ovata and the right valves of C. 

 parvirostris, were entirely wanting. It appears also that Prof. Hall's description 

 was drawn from a right valve. The idea, however, that the two sets of valves 

 might really belong to one species, would not probably have been entertained 

 but for the discovery of a specimen with both valves in closely fitting juxtapo- 

 sition. On one side the specimen is C. ovata, on the other C. parvirostris ! 

 The beaks of the two valves are wanting, but the ventral margins apply to each 

 other with exactitude, the number of radiating lines in a given distance being 

 the same on the two sides. 



From the same exhaustless deposits of fossil remains, Mr. White's industry 

 has brought to light some other forms which present similar characteristics. 



It is evident that these fossils cannot be referred to any known genus. It is 

 doubtful whether they fall within the limits of any recognized family assem- 

 blage. Judging from their analogies, they must have been asiphonal, integro- 

 pallial Pleuroconchs, though little evidence of the possession of a byssus has 

 been detected. From the inequivalve family Avieulidse (including Aucella, to 

 which they are most related,) they are clearly excluded by the greater ventri- 

 cosity of the right valve, and the absence of an anterior wing and byssal sinus. 

 From the free inequivalve Osircidie their great gibbosity distinguishes them. 

 From Dolabra, McCoy, they differ in the greater ventricosity of the right valve 

 and less transverse shape. 



In view of the facts above recited, though some palaeontologists may not re- 

 gard them as sufficiently conclusive, I have ventured to publish a diagnosis of 

 the supposed new genus. 



Dexiobia Wuitei, Winchell, (= Cardiomorpha ovata, Hall. -(- C. parvirostris, 

 White.) Shell subrotund, with a slight anterior obliquity caused by a mode- 

 rate protrusion of the antero-ventral border, from which, in the right valve, a 

 slight elevation extends to the beak ; anterior margin rather straight above. 

 Hinge-line short, regularly curved ; beaks nearly central. Surface marked by 

 fine radiating ribs becoming obsolete toward the umbo and numerous irreg- 

 ular concentric wrinkles, which are generally mo6t conspicuous in the left 

 valve. 



Height from beak to middle of ventral margin 1-26 (100) ; greatest antero- 

 posterior dimension, nearly bisecting the first measure, 1-16 (92) ; convexity of 

 right valve -45 (35). Height of another specimen 1-67. Height and convexity 

 of a left valve 1-19 (100) and -26 (22). 



Dexiobia Halli, n. sp. Shell small, semi-elliptic, subequilateral. Hinge-line 

 straight, extended ; in some specimens as long as the greatest width of the 

 shell. Right valve extremely ventricose, flattened and subalate toward the 

 hinge extremities ; left valve with a very small obtuse beak, and slender poste- 

 rior cartilage plate bearing a longitudinal median furrow. Surface smooth. 



Height from beak of right valve to middle of ventral side -65 (100) ; length 

 of hinge-line -76 (117) ; ventricosity of right valve -35 (54). 



MYTILUS, Linnseus. 

 Mytilus Whitfieldianus, Win., (Proc. Acad. Nat. Sci. Phil., Sept., 1862, p. 



* Compare also Lucina ? retusa, Hall, (Geol. Rep. 4th Dist., N. Y., p. 245), and Ungulina suborbi- 

 culo.ris, (lb. p. 243). 



1863.] 



