WOQDWAED : ANATOMY OF ADEORBIS. 145 



maximum in AdeorMs, Rissoia, Lamellaria, and Crucihulum (the 

 latter has, however, lost its left zygoneury). Slight differences are 

 found in the three first-named genera in the position of the supra- 

 and sub-intestinal ganglia in relation to the right and left sides of 

 the body, this depending on the relative degree of contraction of 

 the commissures connecting them with the pleural ganglia, but 

 otherwise these three genera closely resemble one another in their 

 nervous system. 



A pair of well-developed otocysts are present, each situated at the 

 postero-dorsal corner of one of the pedal ganglia, and each containing 

 one otolith. I was unable to trace their innervation. 



The eyes, as stated above, are extremely small, and an examination 

 of sections shows that they are vestigial structures, being reduced to 

 a minute mass of pigment devoid of all nervous and dioptric structures. 



Ajjinities. — Adeorhis subcarinatus was originally described by 

 Montagu under the name Helix suhcarinclta, the genus Adeorhis being 

 founded in 1842 by Searles Y. Wood, who placed it between the 

 genera Margarita and Natica; Philippi in 1844 placed it in the 

 Paludinacea, between Fossarus and SJcenea. The most striking change, 

 however, was introduced by Gray, who in 1 847 placed this Gastropod 

 with the Trochidse. Gray's view was adopted by Adams, Chenu, 

 Zittel, and S. P. "Woodward ; the last-named, however, placed Adeorhis 

 nearer the Turbinidse. Deshayes [2] in 1861 was the first observer to 

 examine the living animal, and he states that it is certainly neither 

 a Trochus nor a Turho, but that it is either allied to the Rissoiidee 

 or constitutes a distinct type from all known forms. Gwyn Jeffreys, 

 who was the first to examine the operculum, placed Adeorhis with 

 the Solariidse, a view which was accepted by Tryon (Man. Conch ) 

 in 1883. 



It was not, however, till 1885, when Fischer [4J examined the 

 radula, that Adeorhis was definitely proved to belong to the 

 Tsenioglossa, and he concludes that it has affinities with Rissoia, 

 while in its conchological characters it approaches Skenea. In view 

 of Fischer's work it is difficult to understand why Bucquoy, 

 Dautzenberg, and Dollfus [11] still place the family Adeorbidae 

 between the Turbinidae and the Haliotidee, especially when they 

 themselves state that Fischer has definitely shown Adeorhis to be 

 Tsenioglossate. 



It will be seen from the above that there has been a considerable 

 difference of opinion in the past regarding the systematic position 

 of Adeorhis, the most generally accepted view being that it finds its 

 nearest allies in the Rissoiidse. 



A comparison of the animal and its organs with other Prosobranchs 

 brings us to the following conclusions : — Adeorhis is a typical 

 Tsenioglossate, as shown by its radula, which most nearly resembles 

 that of Rissoia, while differing therefrom in the character of the 

 median tooth, and which is totally unlike the Naticoid radula. The 

 operculum is Littorinoid as in Rissoia, some Naticoids, and so many 

 other Tsenioglossa, but it is unlike that of Skenea; the characters 

 of the foot, gill, and tentacular appendage suggest the similar organs 



