FISTULANA. 



other GastrochcencEy because in that species the anterior 

 extremity of the two internal valves is more produced 

 than in most other species of the Genus : the G. mytiloides 

 of Lam. being however, still more so, though not other- 

 wise so nearly allied to Fistulana Clava, Notwithstanding 

 the differences last mentioned, it is not without some hesi- 

 tation that we allow Fistulana a place as a Genus, because 

 the only species we can admit is so nearly allied to and 

 has already been associated with Gastrochcena under the 

 same generic appellation; the principal considerations 

 that have induced us to adopt this conclusion are, 1st. the 

 obligation we feel ourselves under to account for every 

 Lamarckian Genus, and 2ndly, the very peculiar charac- 

 ters which distinguish this, and which by most naturalists 

 will be thought sufficient to entitle it to that rank. 



We do not advert to any of Lamarck's observations 

 on the animal of Fistulana, because it does not appear 

 that he had ever seen the animal of the only species we 

 can admit to a place in it. 



Shell equivalve, inequilateral, gaping widely at the 

 basal margin, with the anterior side very short. The two 

 valves united by a ligament and included in the lower 

 part of a shelly tube, which is closed at the anterior (in- 

 ferior) extremity > attenuated and open at the posterior. 



Fig. 1. Fistulana Clava, showing the tube without a septum. 



2. " showing a septum. 



3. outside of the valves. 



4. inside of the valves. 



