REPOET ON THE PTEROPODA. 
27 
tin. Furthermore, the spire is proportionally much shorter in Limacina trochiformis, 
ancl the operculum has a form differing from that of all the other species in the large 
extent of its spiral portion (three-sevenths) and in the convexity of its columellar margin. 1 2 
In Limacina australis 2 the columellar margin of this operculum is almost rectilinear, and 
the spiral portion hardly attains to more than a third of the total length. Limacina 
trochiformis has certainly less affinity with Limacina australis than Limacina lesueuri, 
in spite of the depressed spiral of the latter. 
As to Limacina retroversa, it is certainly more nearly allied to Limacina australis 
than Limacina trochiformis, but the characters which distinguish it from that form are 
quite distinct enough to be recognised as specific. Thus the umbilicus of Limacina 
retroversa, while quite distinct, is very narrow", 3 in contrast to that of Limacina australis, 
which as w r e have seen is very broad. 4 The spire is pointed in Limacina retroversa, but 
obtuse in Limacina australis, where the whorls are besides more convex, less numerous, 
and separated by a shallower suture. Even at first sight Limacina australis is 
distinguished from Limacina retroversa by the expansion of the last coil and by its 
projection beyond those in front. Finally, in Limacina retroversa the spiral portion of 
the operculum is much more reduced than that of Limacina australis .* 
8. Limacina retroversa (Fleming). 
1788. (!) Turbo lunar is, Gmelin, Systema naturae, i. p. 3587. 
1823. Heterofusus retroversus, Fleming, On a reversed species of Eusus, Mem. Wern. Nat. 
Hist. Soc., vol. iv. p. 498, pi. xv. fig. 2. 
1841. Limacina balea, Mpller, Bemaerkninger til slaegten Limacina, Krpyer, Nat. Hist. 
Tidsskr., 1 Raekke, Bd. iii. p. 489. 
1844. Peracle flemingii, Forbes, in Thompson, Report on the Fauna of Ireland, Rep. Brit. Assoc., 
1843, p. 249. 
1844. Sc sea stenogyra, Philippi, Fauna Molluscorum u triusque Sicilise, p. 164, pi. xxv. 
fig. 20. 
1846. Spirialis stenogyra, Loven, Index Molluscorum litora Scandinaviae occidentalia habitantium, 
Oversigt k. Vetensk.-Akad. Forhandl., 1846, p. 4. 
1849. Spirialis femingii and Spirialis macandrei, Forbes and Hanley, History of the British 
Mollusca and their Shells, vol. ii. pp. 384, 385, pi. lvii. figs. 4, 
5,: 6, 7. 
1849. (1) Spirialis jeffreysii, Forbes and Hanley, Ibid., vol. ii. p. 386, pi. lvii. fig.,8. 
1850. Limacina retroversa, Gray, Catalogue of the Mollusca in the collection of the British 
Museum, pt. 2, Pteropoda, p. 33. 
1 Souleyet, Voyage de la Bonite, Zoologie, Mollusques, pi. xiii. fig. 33. 
2 Souleyet, Ibid., pi. xiii. fig. 24. 
3 Sars, Mollusca regionis arcticse Norvegise, pi. 29, figs. 2c, 36. 
4 Souleyet, Voyage de la Bonite, Zoologie, Mollusques, pi. xiii. fig. 23. 
6 Sars, Mollusca regionis arcticse Norvegise, pi. 29, figs. 2 d, 3 d. 
