374 Mr. E. A. Smitli on the Genera 



to add that the nucleus is central, and, in character, the 

 operculum is similar to that of Turritella, which is also 

 multispiral, and not paucispiral, like that of Mesalia. The 

 genus will include Turntella re^icwZa^a, Mighels & Adams, 

 T. ei'osa, Couthouj, T. eschrichiii, MiddendortF, Mesalia 

 lacteola, Carpenter. 



All of these species have an arctic appearance, being 

 chalky white, and clothed with a thin yellowish-olivaceous 

 periostracum, differing in this respect from Turritella, which 

 exhibits scarcely any traces of it, or might even be described 

 as devoid of it. 



The radulae of 2\ reticulata and T. erosa are of the same 

 character as that of Turritella, and the differences noticeable 

 are probably merely specific. 



The base of the aperture in Tachyrhynchus exhibits more 

 or less of a sinus, it being most distinctly shown in T. lacteola^ 

 Cpr. In Turritella there is no such emargination or effusion. 



Tachyrhynchus is at once separable from Mesalia by the 

 different operculum, and its boreal character. Like Turri- 

 tella, Mesalia exhibits usually only very faint indications of 

 the periostracum. 



Tachyrhynchus erosa (Couthouy) . 



1838. Turritella erosa, Couthouy, Boston Journ. Nat. Hist. vol. ii. 



p. 103, pi. iii. fig. 1. 

 18-41. Txirritella erosa : Gould, Invert. Massachusetts, p. 267. 

 1842. Turritella 2>olaris (Beck MSS.), Mciller, Index Moll. Greenland. 



p. 10. 

 1849. T'lirritella erosa : Middendorff, Malac. Ross. p. 68. 

 1852. Turritella erosa : Mcirch, Cat. Conch. Yoldi, p. 54. 

 1857. Turritella erosa : Mcirch, llink's Gronland, vol. ii., Naturhist. 



Bidrag, p. 82. 

 1868. Tachyrynchus erosa : Morch, Amer. Journ. Conch, vol. iv. p. 46, 



animal. 



1870. lurritella erosa : Gould, Invert. Massachusetts, ed. 2, p. 317, 

 fig. 585. 



1871. Mesalia polaris: Dall, Amer. Journ. Conch, vol. vii. p. 118. 

 1877. Turritella erosa : Jeft'reys, Ann. & Mag. Nat. Hist. vol. xix. 



p. 239. 

 18tfo. Turritella erosa: Aurivillius, Vega-Exped. vol. iv. p. 322, pi. xii. 



fig. 7, pi. xiii. fig. 17 (radula). 

 1886. Turritella (TurHtellopsis) erosa: Tryon, Man. Conch, vol. viii. 



p. 208. ^ 



Hah. Massachusetts (^Couthouy S) Gould) ; Maine {Blaney) ; 

 Labrador (Bush) ; Greenland {Moller) ; Davis Straits 

 (' Valorous^ ExjJed.) ; Nova Scotia [Brit. Mus.). 



The operculum of this species is described by Morch as 

 similar to that of reticulata, and a specimen in the British 

 Museum confirms his description : " Horny, yellow, orbicular, 



