i: KI'TILIAN AGE. J U R A 8SIC PE RIOD. 85 



Genus VO I. si. 1. 1. A, Srorou. 1 



Sy*o. \ r oltrlla, Scorou, Intr. Hist. Nat. 1777, 397. MODED, K. Vet. Ao. Uaiidl. 1793, 392. GRAJ, Proceed. Zool. 



800. 1.1.11,1. 1-47. r.'T. 



Tamariiulifi-rmii, MlDMB. (part), Mas. OIRVKS, 1787, 412. 

 Callitlricht and Call-in, -h.-lmna (gp.), POLI, Utr. Slo. I, 1791, 194. 



JUodiolu*, LAMK. Prodr. 17!)i), h7. CI-VIEB, Ant. Comp. 1800; Begne An. II, 1817, 471 ; nd ib. Ill, 1830, 

 r.\'\. I.I.VK, Rest. Samml. Ill, 1807, 146. OOLDF. Zool. 1820, 611. RIMO, Hist. IV, 1820, 323. FORBM, 

 Mai. Mou. 1838, 43, &o. 



V.,/,i, LAMK. Syst. An. 1801, 113; ID. An. dn Una. VI, 1805, 119; nd Ilist. VI, 1819, 109 Fuou. 



Tab. Sjrat. 1821, p. xlli. BLAIBV. ("ModioU"), Diet. Bci. Nat. XXXII, 1824, 318. BBOVK, Leth. 1837, 

 355, &c. Ac. 



Amyydatum, MriiLF. Entw. 1811, 69. 



Mytiltu (ep.), SOIICM. Ensai, 1817, 106, and various others. 

 llrachyalontt*, 8w AltiKOK, Malacol. 1840, 384. 

 Klym. Vnliella, a kind of forceps or tweezers. 

 Type. Mytilus modiolia, Lix.i. 



Shell transversely oblong; surface smooth, concentrically striate, or with radiat- 

 ing or divaricating stria; or costse ; epidermis often produced into long filaments. 

 Beaks depressed, and placed near the anterior extremity. Hinge sometimes a 

 little callous and crenated, but without proper teeth; ligament linear, occupying a 

 marginal groove. Muscular impressions very unequal ; pallial line faintly marked. 



Animal with mantle margins open, plain, protruding in the branchial region ; 

 anal tubes short, more or less complete ; palpi triangular ; byssus fine and strong. 



This genus, as here defined, embraces two sections or subgenera: 1. The typical 

 species, with a smooth or striate surface, and a non-crenatcd hinge ; 2. Species with 

 radiating or divaricating costce or stria*, and a crenated hinge-margin (Brac/iydotites, 

 Swains.). Adula, of H. & A. Adams, is also sometimes included as a third section, 

 but it seems to be sufficiently distinct to rank as a separate genus. 



The genus Voleelia, or Modiolus, is nearly related to Mytilus, but differs in having 

 the beaks obtuse and placed more or less back from the anterior end, instead of 

 being pointed and quite terminal. The antero-basal region of these shells is also 

 always more prominent than in the Mytili. There are likewise some differences in 

 tin' habits of these two genera. 



Species have been referred to this genus from the Silurian rocks, but they doubt- 

 less all belong to Modiolopsis, OrtJionota, and other extinct genera. 



Several species presenting the external appearance? of VolseUa have also been 

 described from the Devonian and Carboniferous rocks, but we yet want a more 

 accurate knowledge of their hinge and interior, before we can be quite sure they 

 are true Volscllas. The genus seems to be represented in the Triassic rocks, and its 

 existence during the deposition of the Jurassic system of strata is well known. It 



* Scopoli's first species of Volsella was Mytilus modiolus, Lin., the type of the subsequently 

 proposed genus Modiolus, or Modiola, of Lamk. ; while the others belong to the older genus Mytihi* 

 proper, of Lin. As Scopoli was a strictly binomial anthor, however, the law of priority compels us 

 to adopt his name for the previously unnamed group, of which Mytilus modiolutt, Lin., is the type. 

 For a TV;/"/'""'.'/ proposed name cannot be wholly ignored, because the author happened to include 

 some species belonging to an older genus. 



