CREUSIA. 



TESTA compresso-siibconica, valvis quatuor, in- 

 sequalibus, lateraliter ferruminatis, composita ; 

 apice pervio; basi valva testacea, modo calici- 

 formi, modo tubulari, madreporis infixa, clausa : 

 valvae, antica major, caeterae subaequales. Oper- 

 culum bipartitum, valvis quatuor compositum. 



Lepas of tlie Linuean school includes this and all the 

 Lamarckian Cirripedes^ which together certainly form a 

 most natural family. The Genus Creusia was instituted 

 by Leach^ and as he has described it in the " Supplement 

 to Encyclopaedia Britannica," it has been adopted by La- 

 marck ; we also think that there is good reason for adopt- 

 ing the Genus, which may be distinguished from most of 

 the other sessile Cirripedes by its habitat, and from Pyr- 

 goma_, with which it agrees in that particular, by the shell 

 being divided into four parts. We cannot, however, 

 approve of uniting the little shell called by authors Lepas 

 Verruca, and by Leach Clitia striata, (Balanus striatus. 

 Pennant,) with Creusia^ as Lamarck has done, because 

 it differs in every respect, except that of having four 

 valves, which, however, are irregular. 



The shell of Creusia is composed of four unequal 

 valves, united together by their sides; it is generally 

 flat, slightly conical, and perforated at the apex. The 

 base is a deeply cup-shaped, frequently tubular, testace- 

 ous valve, grooved or striated perpendicularly within, 

 and adhering by its lower extremity, or is embedded to 

 its very edge in Madrepores : the aperture of its superior 

 extremity, which is then even with the Madrepore, is. 



