162 Messrs. Alder and Hancock on a new Genus 



liowever it differs in the absence of branchial plumes round the 

 latter organ*. 



Its true position appears to be in the family TritoniadcE and 

 next the genus Eolis, with which it agrees in the form, character 

 and position of the branchife and of the dorsal tentaeula, and in 

 the possession of corneous jaws, and of a true gastro-vascular 

 system. Its form is ovate-oblong, tapering to a point behind ; 

 without cloak, but having a projecting margin dovvii the sides of 

 the back making an approach to the pallial form. The head is 

 anterior and inferior, covered by a small semicircular veil^ from 

 the sides of which arise two short tentacula, held laterally. The 

 dorsal tentacula are linear, erect, and non-retractile ; without 

 sheaths ; behind them are the eyes. The branehise are papillary, 

 and are arranged on the projecting margin down each side of the 

 back. These are united by similar processes continued rovmd the 

 head in front of the dorsal tentacula. The anus is tubular, 

 situated on the medial line of the back near the posterior termi- 

 nation of the branchise, without plumes. Behind this the flat- 

 tened portion of the back terminates and the body tapers down 

 to the tail. The foot is rather expanded at the edges and pro- 

 duced posteriorly. The aperture of the generative organs, which 

 are of the usual form, is on the right side. 



The corneous jaws (present in nearly all the genera of Trito- 

 niadcE, but, as far as we know, never found in the Dorida) are 

 largely developed in this genus, and assume a very complicated 

 structuref. Each jaw (PL II. fig. 3 and 4) consists of a pair 

 of triangular plates, united down the sides and open behind. At 

 the anterior angle is a third plate, not quite one-third the size of 

 the others, which forms a kind of cap over that end, the poste- 

 rior edge standing out considerably from the surface. Under- 

 neath each of the larger plates, at the same end, arises another 

 expansion forming a small segment of an arch. These are united 

 to each other by a corneous strap, which binds the jaws together 

 in front, and acts as a spring to keep the cutting edges asunder 

 when the muscles are relaxed. The whole exposes a large sur- 

 face with many points of support for the insertion of the muscles, 

 indicating the powerful character of these instruments of destruc- 

 tion and the rapacious habits of the animal. The jaws are placed 

 nearly horizontally within the mouth. Beyond them is a strap- 



* We have been kindly favoured l)v J. E. Gva}% Esq. of the British Mu- 

 seum with Leuckhart's description of his genus Idal'ia, to which this bears, 

 at first sight, a considerable resemblance. The same characters, however, 

 that distinguish it from Euplocamus will also sufficiently distinguish it from 

 Idalia. 



•f" The anatomical details, necessarily taken from a single species, may 

 possibly be found to require some slight modification should additional spe- 

 cies 1)0 discovered. 



