40 
THE TOY AGE OF H.M.S. CHALLENGER. 
pods, known by the title Agadina, even when the animals themselves are not known, is 
the horny, perfectly circular operculum of the latter (glassy in the Limacinidse). In the 
operculum of Agadina, furthermore, the coils of the spire have a left-handed twist, and 
increase slowly, so that the nucleus of the spiral is much larger than in the Limacinidse. 
The external surface is also concave ; the aperture is obliquely rounded, with margins 
somewhat expanded, slightly thickened, and united, i.e., the lip and the columellar 
margin are continuous by means of a small callus on the latter, which is absent in 
the Limacinidse. 
But to what streptoneural Gastropods do these larval “Agadina” forms belong? 
The marine left-handed Gastropods are not, indeed, very numerous. But it must be 
remembered that some Gastropods, with right-handed spirals, have their initial portion 
or nucleus twisted to the left. This is not improbably the case with the larval forms in 
question, for there the left-handed twisting of the operculum in all likelihood corre- 
sponds to a right-handed twisting of the shell. 
I. To the group “Agadina” I also refer Atlanta rotundata, d’Orbigny, 1 which Souleyet 
regarded as a variety of Limacina lesueuri (his Spirialis ventricosa). The shell is 
discoidal and flattened ; the spire in no way projects beyond the last coil ; the mouth 
is rounded, and broader than high, with slightly thickened margins. The operculum 
figured by d’Orbigny appears concentric, but as the objects are small and difficult to 
define, it seems to me more likely that the operculum is multispiral, as in the other 
forms of “Agadina.” 
D’Orbigny ’s specimens were obtained in the Pacific Ocean, 36° S., 38° W. This 
form has only been chronicled on one other occasion, by Marrat, 2 on a voyage from South 
America to Liverpool. His specimens are deposited in the Liverpool Museum. 
II. In closing this appendix to the family Limacinidse it is necessary to note 
that the “ Agadina ” forms are not the only left-handed larvae of Gastropods 
which have been taken for Pteropods. The same is true of Limacina turritelloides, 
Boas, 3 the empty shells of which I found in the Challenger collection (Station 
216a, north of New Guinea). By every one familiar with the classification of 
Gastropods, this form would be at once recognised as a young left-handed Cerithium 
( Triforis ), nor have I any doubt that this Limacina turritelloides is identical with 
the form which Craven has described under the title Sinusigera perversa} Like 
Triforis, this exhibited a multispiral operculum, with right-handed twisting. Craven 
has, in fact, subsequently acknowledged 5 that his Sinusigera perversa (from the Indian 
Ocean) is only a pullus of Triforis. 
1 Voyage dans l’Amerique meridionale, t. v. p. 175, pi. xii. figs. 20-24. 
2 On a collection of Pteropods and Heteropods, Ann. and Mag. Nat. Hist., ser. 4, vol. ii. p. 229. 
3 Spolia atlantica, p. 49, pi. iii. fig. 35. 
4 Monographie du genre Sinusigera, Ann. Soc. Malacol. Belg., t. xii. p. 112, pi. iii, fig. 4. 
5 Note sur le genre Sinusigera, Ann. Soc. Malacol. Belg., t. xviii. p. xxvi. 
