370 



MAHtJAL OJF THE 2,10LLtSCA. 



area {h) flat ; deltidium {d) triangular, indistinct ; dorsal valve 

 (Fig. 163) rounded, depre;Lsed; interior with a broad granulated 

 margin; cardinal process piominent, between the dental sockets ; 

 oral processes united, forming a 

 bridge over the small and deep 

 visceral cavity ; disk grooved for 

 the reception of the loop, the 

 grooves separated by branches from 

 a central septum ; loop often un- 

 symmetrical, lobed, and united more 

 or less intimately with the sides of 

 = the grooves; ventral valve {Fig. 1(55) 

 deeply excavated, hinge-teeth pro- 

 minent ; cavities for the adductor 

 («) and pedicle muscles {p) small ; 

 > disk occupied by two large smooth 

 impressions of the cardinal muscles, 

 bordered by a vascular line. 



Animal (Pig. 164) with elongated 



Fig. 165. T. radians. 



oral arms, folded on themselves and fringed with long cirri ; 

 mantle extending to the margin of the Valves and closely ad- 

 herent ; epidermis distinct. 



T. radians is the only unattached species, it is supposed to be 

 fixed by a pedicle when young. (D'Orbigny 



Dorsal valve. Fig. 166. 



a, adductor ; c, crura ; /, loop ; j, Ccirdiiial process ; 



Profile.* 

 p, hinge-plate ; s, dorsal septum 5 



V s, ventral eeptUnj ; t, dental sockets. 



T. hieroglyphicumy Pi. XY., Pig. 12, has a very complicated 

 * The loop (which was discovered by Professor King) has a distinct suture iu tiio 



