76 J. D. MACDONALD ON THE CLASSIFICATION OF THE GASTEROPODA. 
authority ; and even though errors should here and there occur, it is much better, if 
possible, that nothing should be taken for granted merely because it might appear to 
harmonize with a pet theory. 
Malacologists have always been at a loss to ascertain the natural position of Janthina ; 
and the whole truth seems to be this — that it is not correctly referrible to any of the 
families already formed. Even though it should be placed by itself, as has been done by 
several authorities, its true relationship to other families in the series is still a matter of 
doubt. Dr. Gray interposes Janthmidce between the Apple-snails and the Heteropods, 
though the general disposition of authors is to place the solitary genus near Nerita or in 
some neighbouring family. Mr. Woodward has selected the Haliotidce for it, probably 
conceiving that the notch at the outer angle of the shell represented that of Scissurella, 
JPleurotomaria, &c. Taking the anatomy of the animal into consideration, however, it is 
easy to show that this position is most unnatural. It has often suggested itself to me, that 
Janthina was in some particulars related to the Opisthobranchiate families ; and, although 
the affinity is certainly not immediate, I apprehend that it will be difficult to find a better 
place for it than between these and the very natural family composed of the genera Sola- 
rium, Torinia, Scalaria, and perhaps some others. If the latter family, which may be 
named Solariidce, and the Ja/nthinidce are really unisexual, they will form a remarkable 
and beautiful link or passage between the Opisthobranchiata and the unisexual Gasteropoda 
with a lingual ribbon. 
The following extracts from my notes will show that the family of the Solariidce is 
founded on no hypothesis, but on facts : 
" In upwards often fathoms at the Feejee Islands we obtained a small species of Sola- 
rium, apparently quite new. The shell is orbicular, much depressed, witli a wide umbi- 
licus, increasing with the growth of the whorls, and bounded by an angular and minutely 
beaded border, corresponding with the union of the lower and inner walls of the shell. 
This results from the revolution of a small lunated notch at the base of the columella, 
which is perfectly straight, directly joining the body-whorl. The outer lip is thin, and 
slightly angular at its central or more convex part. The mouth of the shell is trapezoidal, 
the angles being situate respectively at the base and summit of the pillar, at the middle 
of the outer lip, and at the union of this latter with the body-whorl. The most interesting 
part of this little shell is discovered on looking down to the bottom of the deep umbilicus, 
in which the sinistral nucleus, smooth, polished- and completely inverted, may be distinctly 
seen. Operculum thin, horny, multispiral, slightly concave externally and minutely 
tuberculated." (The operculum of the typical Solaria is paucispir al . ) 
The animal, in general appearance, much resembles one of Cuvier's Tubulibranchiata. 
The creeping-disc of the foot is small, but the operculigerous lobe is large and subcy- 
lindrical. The tentacula are moderate, conical, with the eyes on the outer side of the 
base. 
a 
" The proboscis is armed with two lateral oral plates, and the tongue with several series 
of tenaculiform teeth, of which the innermost are simple, the external trifid, and the in- 
termediate bifid. Finally, the acoustic capsules contain minute otoconia. 
" Solarium perspectivum. This species occurs plentifully on the sea-side of Kaniba 
