598 PHILOSOPHY OF ZOOLOGY. 



1. TuBiciNKLLA. The form of the shell in this genus 

 is inversely conical, and the apex which constitutes the base 

 is truncated. It consists of a series of horizontal rings, 

 which mark the successive periods of growth, and there are 

 six vertical grooves, which indicate the divisions of the 

 valves. The increase of the shell, with age, in this genus, 

 probably takes place by the addition of a new ring to the 

 mouth. The testaceous plates of the lid are all of equal 

 size. The inferior aperture of the shell is open, or simply 

 closed by the integuments of the cloak. The animal re- 

 sides in the skin of the whale, the lower rings being inserted 

 in the fat, while one or more of the upper ones appear 

 above the cuticle. The T. balanartcm is the only known 

 species. 



In the remaining genera of this family, and the others 

 which follow, the shell is conical, its truncated apex being 

 the mouth ; and its mode of growth such as is detailed in 

 the general remarks on the order. 



2. CoRONULA. The base of the shell is open, but the 

 valves of the lid are unequal in size, the dorsal ones being 

 small. The animals included under this genus likewise in- 

 habit the skin of the whale. Several species of this genus 

 are known. The C. diadema holds a place in the British 

 Fauna. 



3. Chelonobia. In this genus the base of the shell is 

 likewise open, but it differs from the preceding in the plates 

 of the lid being all of equal size. The C. testud'maria, a 

 species which resides on turtles, is the type of the genus. 



4. Balanus. The shell is closed below by a layer of 

 shelly matter, which adheres to foreign bodies, and con- 

 forms to the inequalities of their surface. Nine species arc 

 described as natives of Britain. 



5. Acasta. The base of the shell is cup-shaped. The 

 species reside in sponges^ in the substance of which the base 



