G04 E. J. HARVEY GIBSON ON THE 



foot and of the circular muscle which attaches the foot to the shell on the 

 other. This band of muscle is discontinued at the anterior end for a space 

 equal to about ^th of the circumference ; which space is occupied by the head. 

 The mantle and gill processes are, however, continued round the anterior end, 

 and depend in front of the head. 



The head is distinct, and a slight narrowing indicates a rudimentary neck 

 region. The oral disc (PI. CXLIX. fig. 1), in the centre of which is the oral 

 aperture, is corrugated and kidney-shaped in outline, the hilus being ventral. 

 On either side of the head there is situated a pointed more or less pigmented 

 tentacle (the "nuchal " tentacle), usually from ^ to ^ of an inch long in its con- 

 tracted condition, but, when extended, in large limpets as much as § to an inch 

 in length. On either side of the neck there may be seen an oval yellowish 

 body, the rudimentary gills or ctenidia. They are usually about twice their 

 own length from the circular muscle. They vary in length according to the size 

 of the animal, from ^ 3 to ^ of an inch (PI. CXLIX. fig. 3).* Over the right 

 shoulder may be seen the anal papilla, and the right and left renal papillae, one 

 on either side of it. Ventrally the muscular foot is seen widening as it passes 

 downward, and having a thin rim as its ventral edge. 



On removal of the shell, the visceral dome is exposed, and found to be 

 covered by a deeply pigmented membrane. The colours are deep indigo, 

 streaked with dull yellow. The yellow tinge being due mainly to the subjacent 

 viscera shining through the visceral integument. The superficial dark pigment 

 layer is easily scraped off (PI. CXLIX. fig. 2). 



The muscle connecting the foot and the shell is now visible, on surface view, 

 as a ring, incomplete in front, of uniform width, save at its anterior extremities, 

 which are rather wider and rounded off. The superficial pigment is most 

 abundant near the muscle band. 



The eyes may be made out as minute black specks, one on either nuchal 

 tentacle, on a slight prominence on their outer aspect, near the base. 



General Arrangement of the Viscera. — The general arrangement of the 

 viscera may be made out on removal of the shell, and after the superficial 

 pigment layer of the visceral integument has been scraped off. If the integu- 

 ment itself be removed, the relation of the viscera may be still better defined 

 (PI. CXLIX. fig. 3). The integument must be removed with care, as it is 

 intimately related in some parts to the subjacent tissues. The free edge of the 

 mantle over the cephalic region being also removed, the visceral mass is seen to 

 be bounded anteriorly by a ridge, from which project forwards on the right hand 

 side the anal and renal papillae. From the anal papilla, the rectum passes 

 backwards transversely for a certain distance, and then passes circularly round 



* In the figure they are represented as too near the middle line and too near the base of the tentacle. 



