A RKYISION OF THK AUSTRALIAN Tin HACXA . 



('HAi;i.l> Hl'M.KV. 



(Pliites xwii.-xxxiv., and Kiafiiie 1). 



From the earliest times tlie TridiruK shells, on aeoount of their hii<fe 

 si/.e, have attraeteil the notice of naturalists, so tliat the j)i(ineeis of 

 eoneliology more than a hundred yeais at(o ali-eadv ha.d collected a lai^fe 

 body i)f information about them. Hut modt?rn zooh^gists have not found 

 much inoi-e to add, peihaps because the subject was considei-ed to be 

 exhausted. Yet tlie history of the habits, aHlnities and nomenclature of 

 tliis curious genus is still far from complete. 



A 'rridiiciiii occuring abundantly' in the (lulf of Suez was examined 

 by Dr. Leon Vaillant. He detei'tnined it. probably erroneouslv, as 'VridnnKi 

 elouijittii, Lamarck, and described it' as buried in sand so that the serrate 

 margin of the valves alone projected ami as moored by a profuse byssus 

 haw.ser to the stone beneath ; he adds tliat the bivalve may change its 

 position and even move to a distance. Vaillant concluded that all other 

 members of the genus 'friihicmi have similar habits and disparages those 

 writers and travellers whose observations differ from his own. Thus he 

 doubted the accuracy of the account of the large, fleshy foot given 

 independently by Quoy and Gaimard- and by Woodward.-' ]n reference 

 to the statement that 7'. crvcea lives buried in coral, Vaillant supposes 

 that it could not actually excavate the stone and must thei'efore have been 

 enveloped by an over growth of the living Coral polyps. These views, 

 advanced with so much authority, seemed to have gained general 

 acceptance. 



In Australia, 'I'rnha-iiiiln- do not behave as Vaillant ilescribes. Certain 

 Pacific species do carve holes in stone just as actively as V]iuhi;< does on 

 Furopeaii coasts. Othei' species I'emain on the sui face, either unfastened 

 or clinging to the I'ock by the fool. 



So TiiiJitnui ai'e divisible into the smaller species that burrow and 

 the laiger ones that lie on the surface. Australian burrowing species are 

 7'. iiiu.ciiiiii, 'I'. ehiiKjatK aiul '/'. cnn-t'ii, the great si/.e of the pedal apertuie 

 at once distinguishing any boi er from any perching species ; the non-boring 



1 Vaillant— Ann. Sci. Nat. o Sor. Z.k.I., iv.. ISfi.'j, ),. 71. 



■^ guov .t (iaimard-Vov. A,vtr..lalK', /.i..l., iii., It;^:., ]>. 490, Moll., PI. Ixxx., 

 fig. 3. 



- Woodward— Ann. Mag. Nat. Hist. (2), xv., 1855, jd. 100. 



