Genus 17. ALDERIA,* Allman. 



Corpus ovato-oblongum, sub-convexum, non palliatum. Caput terminale, distinctum, utrinque in 

 lobum lateralum productum. Tentacula nulla. Maxilla nullse. Branchim papillosse, utroque lateri 

 dorsi dispositse. Anus posticus, in line& media dorsi situs. Orificium genitale anticum ad latus 

 dextrum. 



This genus was first described by Professor Allman, in a paper read at the York meeting 

 of the British Association in 1844, and was afterwards published, with a more detailed 

 description, by the same excellent naturalist, in the 'Annals of Natural History' for January, 

 1846. The single species on which it is founded had been previously observed by Professor 

 Loven of Stockholm, who had placed it in the Btiliger of Ehrenberg. M. Loven has since 

 adopted the genus Alderia in his ' Index Molluscorum Scandinavise.' This genus has obvious 

 relationship with Hermcea and Stiliger, from both of which it differs, as well as from the other 

 genera of the order, in the total absence of tentacles. It is also distinguished from the two 

 genera above named, by the more expanded form of the foot, as well as by the position of the 

 anus, which is not placed forward on the back, as in these genera, but occupies a posterior 

 position, similar to that of Proctonotus and Antiopa. In the absence of tentacles, and in the 

 broad reflected sides of the foot, it shows an approach to the Bulla tribe, and likewise to a 

 small Inferobranchiate Mollusk, described by us in the Eighteenth Volume of the 'Annals of 

 Natural History,' and referred, perhaps erroneously, to Pelta of Quatrefages. It appears to 

 us to be also, in some measure, related to Limapontia, which is not only deficient in ten- 

 tacles, but has the buccal apparatus and tongue similar to those of Alderia; and the 

 curious crystalline, spur-like stiletto, in connexion with the reproductive organs, is found in 

 both. Professor Loven remarks of this animal, that it has the branchiae of JEolis, the vent of 

 Doris> and the head and foot of Akera. 



The absence of corneous jaws, as well as the circumstance of its having been found on 

 Ulvse, leave little doubt that Alderia is a vegetable feeder, and this view is confirmed by its 

 gregarious habits. The genus is more nearly amphibious than any other of the tribe, 

 living in salt-marshes or estuaries with a muddy bottom, and only partially overflowed by the 

 tide. 



The body is ovate oblong, rather broad, and not much depressed. The head is terminal 

 and distinct, narrower than the body, and produced into short lobes at the sides. The 

 mouth is without jaws, and has a narrow spinous tongue. There are no tentacles. The eyes 

 are distinct, and placed rather laterally on the narrow posterior part of the head. The 

 branchise, which are papillose or styliform, are arranged in transverse rows on the sides of 

 the back : there are few in front, but they become larger and more numerous behind. The 

 anus is nipple-shaped, and is placed posteriorly on the median line of the back. The foot is 



* Named after one of the authors of this work. 



