MONOGRAPH OF THE GENUS 



TEREBRATULA, 



By G. B. Sowerby, F.L.S., etc. 



Char. Gen. Testa inaequivalvis, sequilatera, ovata vel subtrigona, 

 pediculo brevi, tendineoque affixa ; valva dorsalis postice plus 

 minusve producta, ssepe recurva, apice perforate, foramine vel 

 integro vel incompleto ; cardo dente in utroque latere unico ; valva 

 ventralis intus ossiculo testaceo, gracili, plerumque furcate, varie 

 flexuoso, e cardine nascente instructa. 



Shell inequivalve, equilateral or symmetrical, very variable in 

 general form (the same species varying greatly in its different 

 stages of growth,) being sometimes nearly egg-shaped, sometimes 

 very flat, but generally rather ventricose ; it is attached to sub- 

 marine rocks, stones, corals, shells, &c. by a short tendinous pe- 

 duncle formed of strong, closely united fibres, which are however 

 frequently a little separated at the attached end ; this peduncle 

 passes into the shell through the perforation of the dorsal valve. 

 The posterior apex of the dorsal valve is more or less produced, 

 frequently recurved and perforated at its termination or deeply 

 notched at its anterior edge, with a small curved tooth on each 

 side of its hinge, which fits into a corresponding hollow in the 

 other valve in such a manner that the two valves cannot be sepa- 

 rated without breaking these teeth or the edges of their sockets. 

 The ventral valve is usually less ventricose than the dorsal, its 

 posterior apex is very seldom even slightly produced, it is furnished 

 within with a slender shelly appendage, which is sometimes simple, 

 short, and recurved, sometimes of considerable length, branched 

 and variously bent, so as to form several symmetrical loops : these 

 generally commence on each side of the hinge, but sometimes 

 near the centre of the shell, and they are sometimes united to the 

 shell at other points. In many species the dorsal valve shows a 

 distinct cardinal area somewhat resembling that of Spondylus, and 

 in the centre of this are generally attached two little triangular 



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