332 Dr. Johnston's Contributions to the British Fauna. 



J 



2. P. IMBRICATA. 



2. P. o b Ion go-Ufie arts y Icevis ; squamis quindecim paribus^ ovattSy 

 imbricatisy spinis bremssimis^ deciduis, 



Hab, The sea, under stones between low and high-water 

 mark, common. 



Desc. Body elliptical, depressed, about one inch and a half 

 long, three or four lines broad, rounded and obtuse at each ex- 

 tremity where it is of equal breadth. It is of a cinereous colour on 

 the back, mottled, and marked along each side with a row of small 

 light spots, one to each scale. The head is generally concealed 

 under the anterior scales : it is a red square or rather heart-shaped 

 corneous plate, emarginate in front, furnished with four small 

 eyes. Scales fifteen on each side, imbricate, ovate or kidney- 

 shaped, the anterior nearly circular, variegated with blackish 

 irregular markings, and thickly punctured with small circular 

 white dots. When first examined they appear smooth, but they 

 are in fact covered with very short spines or processes visible only 

 in certain lights or near the margin. Each scale is fixed to a little 

 fleshy papilla on the back, the rest of the scale being detached. 

 There are about twenty tentacular filaments on each side, with a 

 dark ring at the bulb, and blackish about the base. Feet about 

 thirty-five on each side with a single fleshy spine beneath. BriS" 

 ties yellow, stiff and metallic. When the scales are removed the 

 body appears spotted with black, and these spots become quite 

 distinct and regular near the tail, which is terminated by two 

 setaceous filaments. 



This species is subject to considerable variety in colour and in 

 size. I have described it above when full grown, and as it is 

 generally found in this neighbourhood. In many specimens how- 

 ever the head is not concealed by the scales, and these individuals, 

 it is curious, are generally of an uniform ash or chesnut-brown 

 colour, with the scales also destitute of the beautiful variegation 

 and spotting which so decidedly characterise the preceding. I was 

 at one time disposed to consider it a distinct species, but fur- 

 ther enquiries have satisfied me that it can only be considered a 

 variety. 



