ARCA. 171 



stand in the same relation to genera as varieties to spe- 

 cies, is the point at issue. I am not in favour of this 

 intermediate sort of classification, and believe it would 

 lead to unnecessary confusion, and to a redundancy of 

 names for the same object.. "Area (subg. Cucullaza) 

 pectunculoides " is not easy to pronounce, or even to 

 remember, on account of the parenthetical epithet. 

 Such a mode of subgeneric nomenclature appears to me 

 quite opposed to the spirit and simplicity of the bino- 

 mial system ; and it may not be desirable to follow the 

 example of some modern painters in reviving a state of 

 things that has passed away and become obsolete, by 

 now having a pre-Linnean school. The animal of Area 

 constituted the genus Daphne of Poli. 



A. Shell slightly inequivalve : teeth few in number, set either 

 obliquely or in the line of the hinge-plate, and arranged 

 in two rows, one at each end of the plate, besides nume- 

 rous crenulations in the middle across the plate. 



1. Arca pectunculoi'des *, Scacchi. 



A. pectunculoides, Scacchi, Ann. civ. d. due Sicil. vi. p. 82. A. raridera- 

 tata, F. & H. ii. p. 241, pi. xlv. f. 8. 



Body reddish-brown : foot long and narrow, when in motion 

 resembling that of a Gasteropod : byssus rather long, horny, 

 and consisting of a single cylindrical thread. 



Shell obliquely rhomboidal, describing in its contour a seg- 

 ment equal to nearly two-thirds of a circle, tumid, thin, rather 

 glossy ; the right valve (or that which has the anterior side to 

 the right hand of the observer) is unmistakeably smaller than 

 the left valve, the margin of which slightly projects and en- 

 closes the opposite valve : sculpture, numerous fine and sharp 

 longitudinal ribs, radiating from the beaks, and equally nume- 

 rous but less raised transverse or concentric ribs, which cross 

 the other striae and give the surface a regularly reticulated 



* Like Pectunculus. 



i2 



