460 Royal Society. 



served that the animal is bisexual, that the eyes, like those of Glaucus 

 and lanthina, are very small and rudimentary, being closely applied to 

 the ganglia of the brain, after the manner of the acoustic sacs, and 

 that both Phyllirrhue and Glaucus agree in possessing two lateral 

 horny jaws, articulated with each other superiorly, and bordered 

 with minute conical teeth. 



In the Glaucidce, the branchiae, which consist of simple papillary 

 projections of the skin, are distributed in an equable manner over 

 the dorsal region of the body ; and any deviation from this arrange- 

 ment would naturally tend, either to a more definite localization, or 

 still further dispersion. It is the latter modification which appears 

 to have taken place in Phylth-rhoe ; so that its respiratory vessels 

 ramify minutely through the common integument, just as the vas- 

 cular trunks analogous to those which break up in the pectinate gill, 

 adapted for aquatic breathing, are subdivided, and spread themselves 

 over the smooth walls of the lung-chamber in Pulmonifera. 



As respects its affinity to the Pteropods, here too the lateral jaws 

 of PhylUrrho'e must be borne in mind, together with the almost com- 

 plete suppression of the organs of vision. It is worthy of note also, 

 that its acoustic capsules contain otokonia, as in Pteropoda, instead 

 of single globular otolitlies like those of Glauciis, and there is some 

 reason to believe that the long tentacula, so called, are the homo- 

 logues of the cephalic fins of Pteropods. 



The particular features of Phyllirrho'e, expressed in the last para- 

 graph, also serve to distinguish it from the Heteropoda, but it some- 

 what approximates this order in the general conformation of its body, 

 which is elongated, laterally compressed, and presents a kind of pro- 

 boscis at the anterior, and a rudder-fin at the posterior extremity. 

 There is also, as it would appear to be, a small remnant of the foot 

 on the inferior thin margin of the body, and the lateral uudulatory 

 motion of the animal in the water exactly resembles that of Cero- 

 phora, or Carinaria. 



The heart of PhyUirrhoiJ, in common with that of Heteropods in 

 general, holds a dorsal position. The auricle lies posterior to the 

 ventricle, as in Ceropliora and Fh-ola, but the reverse is the case in 

 Atlanta and Carinaria, the difference being due to the relation which 

 the respiratory surface bears to the heart itself, lying in every case 

 on the auricular side. Moreover it is remarkable that the rectum 

 is directed backwards in the former instances, but turns forwards in 

 the latter, taking an oj)posite course to that of the circulation 

 through the heart. 



It may be observed in conclusion, that in Heteropoda tlie viscera 

 are closely packed togethor so as to occupy the smallest possible 

 space, while they are widely distributed through the abdomen in 

 Phyllirrhoe ; thus, again, calling to mind its relationship to the 

 Pteropoda. 



This i)aper is illustrated with drawings representing the animal 

 described and some of the details of its internal structure. 



