< I : i i i 1 1 1 1 i } . I li 1 



small, with tubular, abort, anterior anal. Operation) pauciapiral, 



witli Hihceiitral nucleus. 



Animal with elongated loot, truncated in front, when- it form- a 

 duplicature, the Upper margin i mentum of LHV'II l< -- dc\ eloped 

 than the lower; tentacle- Ion--, cylindrical, united ly a -imiated 

 veil, eye- at their exterior la-c ; -nout very .-hurt: OpeTCUligeTOUl 

 lohe simple. 



Dentition < PI. 1<>, fiir. .'>). Central tooth very short, transv- 

 multicuspidate ; lateral tooth also transverse and multicu.-pid ; 

 marginals four, small, transverse, simple (4'1'1'P4;. 



About a hundred living s])ecies are known, all <|iiite small, in- 

 habiting tlu- West QKU' es, Europe, Indian Ocean, Polynesia. Fo-.-il. 

 Tertiary. TriJnmn, Pdainv., I* -Jo, is a synonym. The Trifori- 

 often attains a considerable >i/.e before losing its larval character-, 

 particularly when distant from the shore. Dr. Fischer has captured 

 on the high sea, between Provence and Corsica, a T. j /// rsa, of 

 which the shell had ei^ht or nine whorls, yet the animal still 

 retained its larval vellum. 



An anomaly of the shell is the occasional preservation of a see-on d 

 canal upon the back of the body whorl, showing the termination of 

 a former aperture. This is present in the fossil species upon which 

 Deehayee established hisgenus,and which is named from this character. 

 Dr. Jousseaume, in his recent monograph of the group, divides the 

 species according to the presence or absence of this posterior open- 

 ing, and creates certain new Croups, of his division having three 

 apertures, which he admits are identical in other character- with 

 the .-eetioiis fno and Mtistotn'ii of Hinds, which he places amoim 1 

 those having two apertures. I laving examined several species with 

 three apertures I incline to the opinion that the posterior canal i- 

 only accidentally preserved in some cases by re:i>on of its deflection, 

 which causes its tube to be surrounded wit h shelly matter durini: 

 the growth of the shell, and that it bears no relation to the economy 

 of the animal. This view is fortified by the consideration that 

 neither in this -rronp nor in any other group of the mollusea are we 

 acquainted with any oriran which might occupy or occasion this 

 tube for the purposes of its economy. Moreover, in "lie of the 

 .-pccics before me two individuals possess the third opening, whilst 

 two others have it not. In consequence of this view I relegate Dr. 

 Jouaseatline'a croups /////o/-/x and .IA/x///////r;o/-M to the synonymy of 

 Inn and M<txtnnin respectively. 



