28 
THE YOYAGE OF H.M.S. CHALLENGER. 
1851. Spirialis gouldii , Stimpson, Description of two new species of shells of Massachusetts, 
Proc. Boston Soc. Nat. Hist., vol. iv. p. 8 ; and Shells of New 
England, p. 27, pi. i. fig. 4. 
1857. Eeterofusus balea, Mprch, in Rink, Grpnland geographisk, statistisk og naturhistorisk 
heskrevet, p. 86. 
1872. Eeterofusus alexandri, Verrill, Recent Additions to the Molluscan Fauna of New 
England, &c., Amer. Journ. Sci. and Arts, ser. 3, vol. iii. 
p. 284. 
1878. Spirialis balea and Spirialis retroversa, Sars, Mollusca regionis arcticse Norvegise, 
pp. 329, 330, pi. 29, figs. 2, 3. 
For description and figures see Sars, loc. cit. 
Habitat. — North Atlantic, on the coast of America, from 63° N. (Davis Strait) to 
39° 53' N. (Massachusetts Bay, Verrill); Iceland; coasts of Europe, from Lofoden Island 
to 50° N., though not yet recorded from Behring Straits. 
All records which mention this species as having been found in more southerly 
localities, and notably in the Mediterranean, are erroneous, and ought to apply to 
Limacina trochiformis, with which Limacina retroversa has been confused by Jeffreys, 1 
Weinkauff, 2 Costa, 3 and other conchologists. Limacina retroversa is no longer found in 
the Mediterranean, though it occurs in circa-Mediterranean Pliocene and Quaternary 
deposits (“ Scsea stenogyra ”). 
In the deep-sea deposits this species is found in the North Atlantic over an area 
extending somewhat further south, and it has thus been dredged in the Bay of Biscay by 
the French “ Travailleur ” Expedition (1880). 4 
Observations. — I. Some authorities (Jeffreys, Gould, Sars, Verrill, &c.) regard Hetero- 
fusus retroversa and Limacina balea as two distinct forms. 
Sars supports this in his descriptions and figures. According to him, the two forms 
differ, apart from size which cannot be regarded as distinctive, especially in the fact 
that in Limacina balea the surface is longitudinally striated (parallel to the axis of the 
shell) and that its spire is proportionally longer. 
To the first of these two points, it may be answered that in Limacina retroversa the 
surface also exhibits longitudinal striae, less marked, it is true, but distinctly recognisable, 5 
and that in Scsea stenogyra, Philippi, 6 which Sars identifies with Limacina balea, the 
surface is on the contrary ‘ 4 laevissima.” This point of distinction does not, therefore, 
appear conclusive. 
1 British Conchology, vol. v. p. 116. 
2 Die Conchylien des Mittelmeeres, Bd. ii. p. 486. 
3 Pteropodi della fauna del Regno di Napoli, p. 19. 
4 Jeffreys, The French Deep-sea Exploration in the Bay of Biscay, Rep. Brit. Assoc., 1880, p. 387. 
* Sars, Mollusca regionis arcticse Norvegiae, pi. 29, fig. 3e; Gould, Report on the Invertebrata of Massachusetts, 
ed. 2, pi. xxvii. figs. 345-348. 
6 Philippi, Fauna Molluscorum u triusque Sicilise, pi. xxv. fig. 20. 
