OF SOUTHERN INDIA. 27 



b. Sub-fumUi/,—CLAVAGELLINJS. 



[bryopin^E and clavagellin.e of Tryou, Claoagella, Deshayes). 



Shell with only the right valre free, the left one permanently grown together 

 with the tube. The mantle of the animal must consequently ovei'lap the right 

 valve altogether, causing it to be in some respects internal. 



5. Bnjopa, Gray, 1810, (Tryon, in Proc. Phil. Acad. Nat. Sc. for 1861). 

 Valves generally triangular, unequal ; tube short, posteriorly with a siphonal fringe, 

 anteriorly mostly of irregular shape, enlarged, compressed, in front with a minute 

 fissure. 



5«. Dacosta, Gray, 1858, (see Tryon, loc. clt.), was separated sub-generically 

 to include CI. australis and balanorum, both of which are stated to have no siphonal 

 fringe at the posterior end of the tube; the last named is supposed by Tryon to be 

 only the young of Bri/opa aperta, Sow. 



6. C7fl«a^6'ZZrt, Lam., 1812, (see Deshayes Fossil du bass, de Paris, 2nd edit., 

 1860, vol. i, p. 80, etc.). Valves oval, or sub-oval, nearly equal, short tubuli formed 

 all round the margins of the valves where they come in contact with the tube ; the 

 latter is long and laterally compressed. If an anterior fissure exists, it must be 

 quite irregular and very small. 



7. Stirpnlina, Stol., 1869. Valves ovate, sub-equal, similar to those of Clava- 

 gella, but tubuli formed only at the front part of the tube which has a distinct 

 fissure ; tube long. 



The tri-division of the Lamarckian genus Clavagella was first proposed by the 

 able French conchologist, S. Rang, and afterwards revised by Deshayes in his 

 "Traite clem, de Conchiliologie." In his last edition of the Paris fossils the same 

 author enters upon this question in detail, liut he does not consider the groups suffi- 

 ciently distinct to warrant generic distinctions ; I feel, however, certain that they are 

 equally well definable as scores of others. That passages from one into the other do 

 occiu' is only natural, and must be expected, as the result of further analysis and of 

 om" increasing knowledge, not only in this but in all other similar cases. Palaeonto- 

 logy must greatlj' assist in the discovery of connecting links between forms which 

 appear to be at the present perfectly isolated. The thi-ee genera which I mentioned 

 above are distinct in their habits, connected with some variations in the form of the 

 animals and shells. They all seem to possess the faculty of producing more or less 

 i:)rolonged tubuli, which originate at the edges of the mantle. 



The recent species which have been called by Gray Brijopa generally live in solid 

 rock or coral, and do not, as a rule, secrete tubuli of any great length. Deshayes 

 says, however, that this is entirely owing to local influences, and if it happens 

 that there are any fissures in the rock, a few tubuli are readily formed as observed on 

 fossil species. Such is also the case, he says, with Bry. fClav.) balanorum ; thus we 

 have again a transition from Bryopa to Clavagella, but still partaking more of the 

 general characters of the former than of the latter. 



