1856.] DR. GUNTHER ON A FIERASFER IN A PEARL-OYSTER. 319 
The specimen, which is represented in the accompanying woodcut 
of the natural size, has been in my possession for many years. It 
is an old shell of Margarita margaritifera, in which there is im- 
bedded, behind the impression of the attractor muscle, a perfect 
individual of a fish belonging to the genus Fierasfer. The fish is 
covered by a thin layer of pearl-substance, through which not only 
the general outlines of the body but even the eye and the mouth can 
be seen. ‘The parasitic habits of Fierasfer are well known, and 
Putnam describes, in the ‘ Proceedings of the Boston Society of 
Natural History,’ vol. xvi. 1874, p. 344, a species, Micrasfer dubius, 
which is found on both coasts of Central America, but inhabits 
Holothurians on the Atlantic, and Pearl-Oysters on the Pacific side ; 
and he further mentions, in a footnate, an example belonging to the 
