ORDER II. PEDUNCULATE. 23 



by Dr. Leach, Pyrgoma, Megatrema, Savignium and Adna ; these, how- 

 ever, in accordance with the opinion of Sowerby, we have reunited. The 

 chief peculiarity in the shell of Pyrgoma, and in which it differs from all 

 other Sessile Lepades, is in being composed of only one patelliform 

 piece, somewhat resembling the shell of Fissurella. Like Creusia it is 

 closed beneath by a grooved, cup-shaped or tubular testaceous base, 

 penetrating to some depth in Coral, which is also its peculiar place of 

 habitation. 



Examples. 



PI. X. Fig. 1 to 6. 



Pyrgoma crenatum, Sowerby, Genera of Shells, No. 18. 

 Savignium crenatum, Leach, MSS. Brit. Mus. 



PI. X. Fig. 7. 



Pyrgoma Anglicum, Sowerby, Genera of Shells, No. 18. 

 Adna Anglica, Leach, MSS. Brit. Mus. 



Order II. LEPADES PEDUNCULATE. 



Corpus pedunculo flexili, tendineo, elevatum ; ad basem affixo. 



There is evidently a strong and peculiar analogy in the organization of 

 the Sessile and Pedunculated Lepades ; we are not, therefore, surprised 

 that Linnaeus should have considered it sufficient to have included thern 

 in one common genus. Since his time, however, the Animal Kingdom 

 has been submitted to a more extended classification ; hence, many 

 of the subdivisions that were then considered merely as genera, have 

 been elevated by later writers to the rank of orders. 



The Pedunculated Lepades are contained in a thick membranaceous 

 integument, having a greater or less number of testaceous pieces attached 

 to it ; it is open in front for the free passage of the numerous fringed ten- 

 tacular cirri, and mounted upon a tendinous flexible peduncle, adhering 



