CONCmi'EIlA. 



445 



porous, the pores leading to canals in tlie outer shell-layer, 

 which, open round the pallial line upon the inner margin ; 

 anterior cartilage-pit deep and conical, posterior shallow ; 

 umbonal cavity turned to the front {u) ; teeth 2, straight, sub- 

 central, the anterior largest, each supporting a crooked muscular 

 apophysis, the first broad, the hinder prominent, tooth-like ; 

 inflections (»i, 7i) 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 (?) 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 apophysis {a) does not nearly fill 

 the corresponding cavity in the lower valve. In H. hi-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 {oi) is possibly a siphonal fold, such as exists 

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

 Clnvagella, and the caudate species of Trigonia. 



The development of processes from the upper valve, for the 



Fig. 237. Longitudinal section ; upper half , |-. Fig. 238. Transverse section, ^. 



Hippurites cornu-vaccinum, Bronn. Salzburg, 

 I, m, n, duplicatures ; u, umbonal cavity of left valve ; r, of right valve ; c, c', car- 

 tilage-pits ; t, t', teeth ; a, a', muscular apophyses ; d, outer shclWayer. Fig. 237 is 

 tiken in the line d b of Fig. 238, cutting only the base of the posterior tooth (f). 

 Fig. 23S is from a larger specimen, at about the level d b 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 the other 

 peculiarities of the Hippurite. The equal growth of the margins 



