30 LINNEAN GENERA. 



and white, spotted in such a manner as is our Magpie, called in some places 

 a Pie-annet, which the people of Lancashire call by no other name than a 

 Tree Goose; which place aforesaid, and those parts adjoining, do so much 

 abound therewith, that one of the best is bought for three pence. For the 

 truth hereof, if any doubt, let them repaire unto me, and I shall satisfy them 

 by the testimonie of good witnesses." Gerard's Herbal, p. 1558. 



The shells of this genus adhere in clusters to rocks, shells, floating wood, 

 and other extraneous marine substances, and being incapable of changing 

 place, are supposed to be true hermaphrodites. 



Genus 3.— PHOL AS. 



Animal an Ascidea ; shell bivalve, divaricatej with several les- 

 ser, differently shaped, accessary ones, at the hinge ; hinges re- 

 curved, united by a cartilage ; in the inside, beneath the hinge, 

 is an incurved projecting tooth. 



Pholas crispata. — The Curled Pholas. Plate V. fig. 

 3. Shell oval, gibbous, pale ochreous-yellow ; part next the 

 hinge obtuse, gaping at both ends ; a longitudinal furrow near 

 the centre of each valve ; one half covered with muricated 

 waved stries and wrinkles, the other substriated. 2 inches long, 

 and 3 broad. Inhabits the British coasts. 



Pholades are found below high water-mark, burrowed in hard clay, lime- 

 atone, and wood, which they perforate in their younger state, and as they 

 increase in size enlarge their habitation. 



The phosphorescent property of the Pholades is very remarkable. They 

 contain a liquor which shines with uncommon splendour in the dark, and il- 

 luminates whatever it touches, or happens to fall upon.* 



"There is," says Dr Priestly, "a remarkable shell-fish called Pholes, 

 which forms for itself holes in different kinds of stone. This fish illuminates 

 the mouth of the person who eats it ; and it is remarked, that contrary to 

 the nature of other fish, which give light when they tend to putrescence, 

 this is more luminous the fresher it is ; and when dried, its light will revive 

 on being moistened either with salt water or fresh ; brandy however imme- 

 diately extinguishes it." f 



It is to be regretted, that the experiments made by chemists on those ani- 

 mals, which have a luminous appearance in the dark, have not been suf- 

 ficiently decisive, to enable us to state the true cause of it ; but there is 

 every reason to believe that it proceeds from phosphorus, which is abun- 

 dant in all animal bodies. 



* Sec Memoirs of the French Academy, 171'2. 

 f Priestly's Optics, page 567. 



I 



