PELONAIAD^. 43 



garded as analogous to certain Sii^htmculidce, and in that point 

 of view the details of their form and structure are of much inte- 

 rest to the naturalist. 



" They are both of a cylindrical shape, having their orifices on 

 the same plane, elevated on papillose eminences at one extremity 

 of the body. No rays or tentacula surround either of the [4- 

 cleft] orifices. Their posterior extremities terminate in a blunt 

 point. They live buried in mud, quite unattached to any other 

 body, and are extremely apathetic animals, presenting scarcely 

 any appearance of motion. 



" We have styled the genus Pelonaia, and define it as follows : — 



" Test cylindrical, unattached. 



"Orifices without rays, on two equal approximated papillose 

 eminences at the anterior extremity. 



" Species I. P. corrugata [PI. E, fig.4. ]. — Test deep brown, 

 much elongated, rudely wrinkled transversely. 



" In the mud-filled cavities of old shells from deep water, An- 

 struther. It has also been taken by Dr. Johnston at Berwick. 

 [Northumberland, Mr. Alder.] 



"Sp. II. P. GLABRA [PL E, fig. 3.].— Test greenish-yellow, 

 smooth, pilose, not nearly so much elongated as the last. 

 " Dredged in seven fathoms water, in mud, Rothesay Bay. 



Anatomy of P. glabra. 



" 1. Muscular System. — The mantle is similar to that of other 

 Ascidice, possessing longitudinal and circular fibres. A strong 

 band of transverse fibres passes round it, immediately below the 

 anal orifice, encroaching on the cavity principally on that side. 

 The chief peculiarity of the mantle is its firm adhesion to the 

 test. 



"2. Digestive and Res2yiratory Systems. — The respiratory 

 opening is of small size, and exhibits no folds or tentacular 

 fringes. The respiratory sac is elongated, cylindrical, contracting 

 rather suddenly towards one side to become continuous with the 

 oesophagus. On the external surface of the sac there are about 

 thirty parallel transverse ridges, which give it the appearance of 

 a plaited frill. These plaits are less apparent along the course of 

 the branchial artery and branchial vein, but midway between 



