168 Traiisactions. — Zoology. 



end at the sides of the head, in about a straight Hue with the 

 disc of the mouth. 



2. The convolutions of the intestine are somewhat different 

 to those shown by Cuvier, fig. 12 ; but I have not been able 

 to distinguish any expanded part of the intestine representing 

 the stomach, further than that containing the coils of the 

 odontophore. 



3. The nervous system in Patella vulyata consists of a 

 large ganglion, as shown in Cuvier, fig. 16, from which nerve- 

 fibres go off to all parts of the body. In Patinella radians it 

 will be shown that there are three separate ganglia, connected 

 to one another by thick commissures. There are the pedal 

 ganglia, consisting of two thick masses on the upper surface of 

 the foot. There are two parieto-splanchnic ganglia connected 

 by a commissure going over the back, and by two other com- 

 missures connecting them with the pedal ganglia. These 

 ganglia give off nerves to the somatic cavity, mantle, and bran- 

 chiffi. The cerebral ganglia are situated in the head, and are 

 conuected with the parieto-splanchnic ganglia by commissures, 

 and there are small ganglia on their course where the nerves go 

 out to the tentacles. This nervous system shows that our 

 southern species (as most southern forms are) is a more primary 

 and older form than the northern species. This, I think, is the 

 distinguishing characteristic of Paiinella radians. 



The shell is ovate and moderately convex ; the apex is 

 situated about a third of the length of the shell from the anterior 

 end. The ribs in it are small, slightly rounded, and radiate out 

 from the apex to the margin of the shell. They are intersected 

 round the margin with short ribs extending only about half-way 

 up the shell. The ribs are of a dark-brown colour, and the 

 interspaces are of an ash colour. In the interior of the shell, 

 the upper part, above the circular muscle, is of a dark-brown 

 colour ; below the circular muscle it has a nacreous appearance, 

 having small grooves corresponding to the ribs on the outside, 

 which at the margin are shghtly flattened out, giving the rim of 

 the shell a slightly serrated appearance. 



The head consists of a large fleshy mass (shown in fig. 2, 

 a, h,) slightly narrowed at the neck ; at the sides of the head are 

 two well-marked tentacles, thick at their bases and tapering 

 towards the points, very much of the shape of horns [x, ;/, fig. 

 3). I have not been able to recognise the eyes, at the bases 

 referred to by Woodward, page 278. The mouth opens on the 

 lower surface of the body (it is shown, c, fig. 1), it is simply a 

 large oval-shaped sucking-disc. 



The foot is a large olive-coloured oval disc, covering the 

 lower surface of the body ; by means of this muscular foot, the 

 animal attaches itself to rocks ; the free edge of the mantle 

 hangs doAvn round it. 



