ORDER I. SESSILES. 15 



Order I. LEPADES SESSILES. 



Corpus, pedunculo nullo, in testa ad basem affixa inclusum. 



The Sessile Lepades are contained in a circular coniform shell, con- 

 sisting of several solid calcareous pieces united together at the sides, and 

 fixed immediately at the base, which is either testaceous or membrana- 

 ceous, upon some marine substance ; and they have a moveable opercu- 

 lum at the top inserted within the aperture, composed of two or more 

 testaceous pieces, separable at the will of the animal for the passage of 

 the tentacular cirri. We divide them into ten genera as follows : 



tubicinella. conia. 



coronula. balanus. 



Elmineus. Clitea. 



Catophragmus. Creusia. 



octomeris. pyrgoma. 



TUBICINELLA, Lamarck. 



Testa cylindraceo-tubulosa, subrecta, valvis sex longitudinaliter ferru- 

 minatis composita, extiis longitudinaliter striata, costis transversis 

 annulatim cincta, utrinque truncata ; basi membrana clausa. Oper- 

 culum cmadrivalve, valvulis apice attenuatis, rotundatis. 



The Tubicinella has a cylindrical tubular shell, nearly straight, trun- 

 cated at both ends, and slightly attenuated towards the base, which is 

 closed by a thin membrane ; it is composed of six longitudinal valves, 

 striated on the outside, and encircled with an irregular number of trans- 

 verse ribs, supposed to indicate different periods of growth, each in its 

 turn having formed the margin of the aperture. The valves of the 

 operculum are trapezoidal and obtuse, inserted in the orbicular aperture 



