FAMILY I. TUBICOLA. 35 



Serpula penis, Linnseus. 

 Serpula aquaria, Dillwyn. 

 Penicillus Javanus, Bruguiere. 



CLAVAGELLA, Lamarck. 



Testa inasquivalvis, ina?quilateralis ; valva altera in pariete inferiori tubi 

 testacei conferruminata, altera libera intra, tubum testaceum ad 

 musculum animalis adhae rente ; tubo inferne in clavam ovatam, vel 

 cameram subcompressam, tubulis spiniformis irregularibus echina- 

 tam, terminato ; superne subattenuato et aperto, margine late re- 

 flexo. 



The Clavagella is an animal of considerable interest and importance, 

 as it forms a remarkable link between the Aspergillum and Fistulana, 

 confirming the propriety of arranging the former with the Tubicola. In 

 Aspergillum, as we have already noted, the bivalve shell is entirely im- 

 bedded in the side of the tube ; in Fistulana it will be observed that the 

 shell is altogether free within the tube and quite independent of it ; but 

 in Clavagella, one valve of the shell is imbedded in the side of the tube, 

 and the other free or independent of it, attached to the muscle of the 

 animal : thus we have clearly an intermediate form partaking of the prin- 

 cipal characters of each of those genera. 



The tube of Clavagella, which is found buried in stone with the cla- 

 vate or chambered end downwards, has a kind of perforated plate in- 

 serted at the bottom, analogous to the terminal disc of the tube in Asper- 

 gillum; it is also surrounded with minute spiniform tubes, probably filled 

 also with certain fleshy filaments of the mantle : at the side of this cham- 

 ber is imbedded the fixed valve, somewhat pearly in appearance ; and 

 attached to the animal by two strong adductor muscles is the correspond- 

 ing one, hinging upon the other by a soft coriaceous ligament. 



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