CONCHIFERA. 



445 



porous, the pores Ipading to canals in the outer shell-layer, 

 which open round the pallial line upon the inner margin ; 

 interior cartilage-pit deep and conical, posterior shallow ; 

 ambonal cavity turned to the front (w) ; teeth 2, straight, sub- 

 central, the anterior largest, each supporting a crooked muscuUvr 

 apophysis, the first broad, the hinder prominent, tooth-ilk e ; 

 inflections (m, n) surrounded by deep channels. 



H. cornu-vaccinum attains a length of more than a foot, and 

 is curved like a cow's horn; the outer layer separates readily 

 from the core, which is furrowed longitudinally. The ligamental 

 inflection {I) is very deep and narrow, and the anterior tooth 

 farther removed from the side than in H. hi-oculatus and radiosus 

 (Figs. 233, 234) ; the posterior apophyd£ (a) does not nearly fill 

 the corresponding cavity in the lower v^lve. In H. bi-oculatus 

 and some other species there is no ligamental ridge inside ; 

 these, when they have lost their inner layer, present a cylin- 

 drical cavity with two parallel ridges, extending down one side. 

 The third inflection (n) is possibly a siphonal fold, such as exists 

 in the tube of Teredo, and sometimes in the valves of PJwlas, 

 Clavagella, and the caudate species of Trigonia. 



The development of processes from the upper valve, for the 



P-'-'. 237. Longitudinal section ; upper half, |. Fig. 233. Transverse section, j. 

 Hippurites cornu-vaccinum, Bronn. Salzburg, 

 I, m. n, auplicatures ; u, umbonal cavity of left valve ; r, of right valve ; c, c\ car- 

 tuage-pics ; t, t\ teeth ; a, a\ muscular apophyses ; d, outer sheU-layer. Fig. 237 is 

 ti^ken in tlie line i b oi Fig. 23S, cutting only the base of the posterior tooth («';. 

 Fig. 238 is from a laager specimen, at about tlie level db oi Fig. 237, cutting the point 

 of the posterior apophysis (a'), and showing the peculiar shell-texture deposited by 

 the anterior adductor (a). 



attachment of the adductor muscles harmonises with ^he other 

 peculiarities of t]\e Hipp^^rite. The equal growth of the margin-s 



