Genus 18. PROCTONOTUS,* Alder and Hancock. 



Corpus ovato-oblongum, depressum, postice acuminatum. Caput subinferius, velo parvo, semi- 

 lunar^ obtectum. Maxillse cornese. Tentacula 4, quorum 2 majora, linearia, dorsalia, et 2 minora, ad 

 marginem veli disposita. Branchia papillosse, elongatse vel ovatse, ad marginem lateralem prominentem 

 dorsi ordinatse, et anteriiis circum caput collocatse. Anus posticus, in linea media dorsi situs. 

 Apertura genitale ad latus dextrum. 



On introducing this genus to the notice of naturalists in the 'Annals of Natural History' 

 for March, 1844, we proposed for it the name of Venilia; but becoming aware soon afterwards 

 that the name had, a short time previously, been appropriated in Morton's ' Synopsis of the 

 Chalk Fossils of the United States,' to a genus of bivalves, we substituted for it the present 

 appellation ; announcing the alteration in the following May number of the same journal. 



This genus unites some of the characters of the Doridida with those of the jEolidida, 

 showing an approach to the former family in the broad and subdepressed form of the body, 

 the rudimentary cloak, and the position of the vent. Its relationship with Triopa, in that 

 family, is evinced not only by the general form of the body, but likewise by the shape of the 

 head, by the position of the oral tentacles, and by the marginal processes, the situation of 

 which in Triqpa resembles not a little that of the branchial papilla? of Proctonotus. The true 

 place of this genus, however, is in the Eolididcs, where it forms the centre of a small group of 

 genera, mostly of recent discovery, in which the dorsal anus, and other characters indicating 

 a departure from the Eolidian type, are more or less developed. 



The Zephyrina of Quatrefages has been supposed to be synonymous with this genus ; 

 but it appears to differ in having four linear tentacles visible from above as in JEolis ; and as 

 M. de Quatrefages is uncertain with respect to the position of the anus, the true place of 

 Zepliyrina can scarcely be fixed with certainty until some further information concerning it is 

 obtained. 



The body of Proctonotus is ovate-oblong, subdepressed, and tapering to a point behind. 

 There is no distinct cloak ; but there is a projecting margin on the sides of the back, making 

 an approach to the pallial form. The head is inferior, and covered with a small semicircular 

 veil ; from its sides proceed two short oral tentacles. There are two dorsal tentacles placed 

 in the usual position. They are linear and non-retractile. The mouth is furnished with a 

 pair of strong corneous jaws, and a rather broad, denticulated tongue. The branchiae are 

 large, papillary, and ovate ; having an extremely small central gland, reaching scarcely half 

 the length of the papilla. They are arranged down the produced sides of the back and 

 round the head in front. The anus is tubular, and situated in the median line of the back, 

 near the posterior termination of the branchiae, behind which the body tapers to the tail. 

 The foot is rather broad, expanded at the edges, and produced posteriorly. The aperture of 

 the genital organs is placed a little in advance of the centre of the body on the right side. 



* From npoKTog, anus, and vmtoq, dorsum. 



