HETEROFUSUS. 505 



ings ; two fin-like expansions, elongate, rounded, and united at tUeir 

 base by an intermediate lobe bearing an operculum. Mantle large, 

 open in front, forming a large gill cavity ; gill internal ; vent on 

 right side of mantle. 



Shell spiral, transparent. Operculum distinct, spiral, vitreous, of 

 few whorls. 



Genus HETEROFUSUS, Fleming. 1825. 



Shell thin, transparent, sinistral, conical, turreted ; spire elon- 

 gate, axis imperforate ; aperture angulated anteriorly, columella 

 smooth, arcuated. 



Heterofusus balea. 



Tlate XXVIL Fig. 349. 



Limacina balea, Moller, Ind. Moll. Gr. 4 (1842). 



Heterofusus balea, Morch, in Rink's Greenl. 86 (1857). — Stimpson, Check Lists, 4 



(1860). 

 Spinalis Gouldii, Stimpson, Proc. Bost. Soc. N. H. iv. 8 (1851) ; Shells of New England, 



27, pi. 1, fig. 4(1851). 



Shell ovate-globose, vitreous, very thin, pellucid, very light, nar- 

 rowly and deeply umbilicated ; spire conoid ; whorls seven, sculp- 

 tured by minute, distant, impressed, revolving lines ; last whorl 

 large ; aperture about equalling the spire, obtuse in front. Length, 

 one tenth of an inch ; breadth, seventy-five thousandths of an inch. 

 Whole coast of New England north of Cape Cod. (^Stimpson.') 



Massachusetts Bay, February to April (^Stimpson) ; Greenland 

 (Moller'). 



The figure which I have given is copied from that of Dr. Stimpson. 



Heterofusus retro versus. 



Plate XXVIL Figs. 345-348. 



Fitsus retroversus, Fleming, Mem. Wern. Soc. iv. 498, pi. 15, fig. 2. 

 Perade Flemingii, Forbes, Brit. Ass. Rep. 1848, 249. 



Spirialis Fleminr/ii, Fokbes and Hanley, Brit. Moll. ii. 384, pi. 57, figs. 4, 5; pi. M. M. 

 fig. 1 (1853). —Alex. Agassiz, Proc. Bost. Soc. N. H. x. 14 (1865). 



With the body whorl very ventricose ; the spire of four whorls, 

 but not forming half the length of the shell. 



The following is copied from the " Boston Proceedings," 1. c. : — 

 Ml-. Alex. Agassiz made a few remarks on the habits of a species 



