INVERTEBRATE PALAEONTOLOGY. 77 



Barbatia, Gray (1840), Syuon. Itiit. Mas., 135; and (1847), Lond. Zool. Proceed., 197. — H. and A. 

 Adams (1857), Gen. Recent Moll., II, 534.— Chenu (1862), Man. Couch., II, 172.— Sto- 

 liczka (1870), Pateont. Indioa, III, :?40. — Conrad (1862), Proceed. Acad. Nat. s,i. Philad., 

 290; and (1873), Appendix to Kerr's N. Carolina Geol. Report (issued in advance), 4. 



Daphnoderma (Poli), Mtirch (1*53), Cat. Yoldi, 40.— H. and A. Adams (1858), Gen. R. Moll., 11,660. 



Aear, Gray (1857); Ann. and Mag. Nat. History, XIX, (2d ser.), 309. — H. and A. Adams (1857), 

 Gen. Recent .Moll., II, 5155 (as a subgenus of Barbatia). — Chenu (1862), Man. Conch., II, 

 173 (as a subgenus of Barbatia). — Stoliczka (1870), l'ahcout. Iudica, III, 340 (as a sub- 

 genus <>f Barbatia). 



Calloarca, Gray (1*57), Aim. and Mag. Nat. Hist., XIX, (2d ser.), 369. — H. and A. Adams (1857), 

 Gen. Recent Moll., II, 535.— Stoliczka (1870), Pala-ont. Iudica, III, 340. 



Siriarca, Conrad (1862), Proceed. Philad. Acad. N. Sci., XIV, 270. 



Granoarca, Conrad (1862), ib. (as a subgenus of Barbatia). 



I Cucullcearca, Con. (1865), Am. Jour. Conch., I, 11. 



Plagiarca, Conrad (1873), Suppl. to Kerr's Geol. Report N. Carolina, 4 (as subgenus Barbatia). 



Pohjiicma, Conrad (1873), ib. (as a subgeuus of Barbatia). 



Etym. — Barbatus, bearded. 

 Type. — Area barbala, Linn. 



Shell varying, according to the sections and species, from transversely 

 elongate-subovate, to rhombic-trapezoidal, moderately or rather strongly con- 

 vex, with ventral margins more or less sinuous and gaping, or sometimes 

 nearly closed anteriorly; surface ornamented with radiating strise or costee, 

 or rarely cancellated, covered with a rough, usually loose, hairy epidermis; 

 ligament-area nearly always very narrow, marked by divaricating, or obliquely, 

 longitudinally, or rarely transversely-arranged cartilage-furrows; hinge gen- 

 erally somewhat arched along the under side, and narrowed at the middle, 

 where the denticles are very short and range vertically, but widening some- 

 what toward the extremities, where they are longer and more oblique. Animal, 

 as in Area, forming a byssus by which it attaches itself to rocks, &c. 



A thorough revision of the Arcidce, including all of the recent and fossil 

 types, would doubtless result in the establishment of other sections of this 

 genus; but, as I am not making an especial study of the family, I prefer to 

 note only such subordinate groups as have already been ranged under it by 

 others. These may be severally distinguished from the typical forms, as well 

 as from each other, as stated below: 



1. barbatia, Gray (typical). 



Shell transversely elougate-subelliptic, or subovate; cardinal mar- 

 gin rounding off, more or less, at the extremities; cardinal area very 

 narrow, with divaricating longitudinal cartilage-furrows. — (Type as 

 already given.) 



