296 TEST ACE A ATLANTIC A. 



it represents more in reality than a slight geographical variety 

 of the European A. bidentata, Mont., with which indeed it has 

 been identified both by Dr. Fischer and Mr. Watson ; though 

 as Pfeiffer, who must have had good opportunities of being 

 acquainted with the latter, has enunciated it lately under the 

 name of Alexia Paivana, I will not do otherwise than treat 

 it as distinct. 



The A, Paivana may easily be recognized, from the other 

 members of the genus which have been found in these various 

 Atlantic archipelagos by its extremely pallid colour (which is 

 usually white with a very faint yellowish tinge), and by its 

 having only a single plait (and that one large, and somewhat 

 inferior in position) on its ventral paries, the oblique colu- 

 rnellary one being the less enlarged of the two. It is rather 

 a small shell for an Auricula, and extremely solid ; its surface, 

 which is nearly opake, is a good deal eaten-into or eroded ; 

 its suture is more or less uneven, or lacerate ; its spire is 

 short, and composed of somewhat fewer whorls than in the 

 generality of the species ; its ultimate volution is slightly 

 elongated ; and the outer lip of its aperture is quite free from 

 denticulations. 



Having given a diagnosis of the various Auriculas which 

 occur in the Madeiran and Canarian archipelagos, I have 

 thought it desirable to compile one for the A. Paivana like- 

 wise, in order to point out more readily in what particular 

 points it differs from the others. 



Seetio II. OPERCULATA. 



Fam.l. TRUNCATELLID^E. 



Genus 1. TRTINCATELLA, Risso. 



7. Truncatella truncatula. 



Cyclostoma truncatulum, Drap. 9 Hist. Nat. dea Moll. 40. t. 1. 



f. 28-31 (1805) 

 Truncatella truncatula, Lowe, Zool. Journ. v. 302. t. 13. 



f. 13-18 (1835) 

 Id., Proc. Zool. Soc. Lond. 217 



(1854) 



Paiva, Mon. Moll. Mad. 162(1867) 

 Watson, Journ. de Conch. 220 



(1876) 



Habitat Salvagem Grandem ; sub lapidibus per litora maris 

 congregans. 



