Zoological Illustrations Series II/Plate 34



This elegantly formed shell is a native of the Red and Indian Seas. It is the most common of the few species retained in the genus Rostellaria; all these are recent; while Hippochrenes has occured only in a fossil state.

The preceding table of affinities, connecting the leading forms among the Strombii, will be adverted to hereafter. At present we shall offer a few observations on the nature of that more comprehensive division of the class Mollusca, to which this particular group appears to belong.

The learned Author of the Horæ Entomologicæ, in that part of his valuable essay relating to the Molluscæ, considers our knowledge of these animals too imperfect to enable him to state the nature of the typical groups: the situations of which, in his diagram of the animal kingdom, are therefore merely indicated by stars. M. Macleay further remarks, that the Gasteropoda of M. Cuvier, with certain restrictions, evidently form a circular group. Yet, from the above omission, it appears he still entertained some doubts on the propriety of this arrangement. Labouring under similar disadvantages to those which impeded the researches of so profound an observer, we feel some hesitation in expressing a different sentiment on the subject, particularly in reference to his own disposition of affinities.

It is evident that these typical groups, whatever may be their nature, must present some very strong points of analogy to those in the circle of Vertebrata: and that such analogies should extend to the corresponding groups of the Annulosa. This we should expect, not only as the necessary result of a truly natural arrangement, but as a primary test, by which the correctness of any series of affinities must be tried. Now admitting that Quadrupeds and Birds shew the same typical perfection among the Vertebrata, as the Mandibulate and Suctorial Insects unquestionably do in the Annulosa, we have two beautiful analogies between these otherwise dissimilar groups, taken from one of the most important functions of nature. Quadrupeds and mandibulate insects are provided with jaws for tearing and masticating their prey, while in birds and suctorial insects, the mouth is lengthened into a proboscis, by which nourishment is imbibed by suction. These analogies are equally conspicuous among the Molluscæ. The Phytiphages of Lamarck (of which the garden snail is a good example), are furnished with jaws and masticate their food: the Zoophages of the same accurate observer, have their mouth elongated into a retractile trunk or proboscis, by which they pierce through other shells, and suck the juices of the inhabitant. To insist on the importance of these distinctions, employed as they have been to characterize primary divisions, is surely unnecessary. That they will be subject to considerable modification, in the subordinate groups, may naturally be expected: but we refrain at present from offering an opinion on the nature of such groups, dependant, as they must be, on greater anatomical knowledge than we yet possess. Nevertheless, until more direct analogies are discovered, than those here stated, we feel some confidence in employing them as typical distinctions of the two great divisions of Gastropod Mollusca.