368 



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

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

 phora, or Carinaria. 



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

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

 ventricle, as in Cerophora and Firola, 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 opposite course to that of the circulation 

 through the heart. 



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

 are closely packed together 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 paper is illustrated with drawings representing the animal 

 described and some of the details of its internal structure. 



IV. "Brief sketch of the Anatomy of a new genus of pelagic 

 Gasteropoda, named Jasonilla" By JOHN DENIS MAC- 

 DONALD, Esq., R.N. Communicated by Sir W. BURNETT, 

 K.C.B. Received March 30, 1855. 



This communication refers to a remarkable genus of pelagic Gas- 

 teropoda, characterized, like Macgillivraya and Cheletropis, by the 

 presence of ciliated cephalic appendages, but having, as in the pre- 

 sent instance, a beautifully transparent, cartilaginous and perfectly 

 symmetrical shell. The author has seen but one species, which was 

 frequently taken between Port Jackson and the Isle of Pines. 



The shell resembles that of Argonauta in shape, is less than one- 

 eighth of an inch in diameter, and the little animal, when fully re- 

 tracted, occupies but a small portion of its cavity. The margin of 

 the mantle is of considerable thickness, containing loosely-packed 

 cells, similar to those of the middle or operculigerous lobe of many 

 Pteropods. About eight ciliated arms, identical in character with those 

 of Macgillivraya, &c., encircle the head, including the mouth, which 



