324 



GENERAL SUMMARY TO 



Waldheimia flavescens (after Hancock). 



M, Ventral valve ; n, dorsal valve ; I, loop ; v, mouth ; z, extremity 

 of intestine; a, adductor; c, divaricators ; c', accessory divaricators; 

 b, ventral adjusters; b', peduncular muscle; b", dorsal adjusters ; 

 P, peduncle. 



done by Blainville 1 and Quenstedt, 2 but the absence of good figures caused much 

 uncertainty to prevail. This deficiency was subsequently supplied by Owen's, Hancock's, 

 and Gratiolet's admirable descriptions and illustrations. The two other pairs have been 

 termed divaricators by Hancock, or cardinal muscles (muscles diducteurs of Gratiolet) ; 

 and have for function the opening of the valves. The divaricators proper are stated by 



Hancock to arise from the ventral 

 valve, one on each side, a little in 

 advance of, and close to the adduc- 

 tors, and, after rapidly diminishing in 

 size, to become attached to the cardinal 

 process, a space or prominence be- 

 tween the sockets in the dorsal valve. 

 The accessory divaricators are, accord- 

 ing to the same authority, a pair of 

 small muscles which have their ends 

 attached to the ventral valve, one on 

 each side of the median line, a little 

 behind the united basis of the adduc- 

 tors, and again to the extreme point 

 of the cardinal process. Two pairs of 

 muscles, apparently connected with the 

 peduncle and its limited movements, have been minutely described by Hancock as having 

 one of their extremities attached to this organ. The dorsal adjustors are attached to the 

 ventral surface of the peduncle, and are again inserted into the hinge-plate in the smaller 

 valve. The ventral adjustors are considered to pass from the inner extremity of the peduncle, 

 and to become attached by one pair of their extremities to the ventral valve, one on each 

 side of, and a little behind the expanded base of the divaricators. The function of these 

 muscles is not only that of erecting the shell, but also that of attaching the peduncle to 

 the shell, and thus steadying the latter on the peduncle. Gratiolet describes the 

 peduncle with great care and states that it is composed of two portions. First of a horny 

 sheath formed of concentric epidermic layers, very analogous to that which Vogt has 

 described in Linr/ula. Second, a fibrous stem enveloped by the sheath. This stem, 

 composed of tendinous fibres, is fixed by its free extremities to rocks, shells, corals, and 

 other marine objects ; the other end passes through the foramen and ends in a 

 bulbous-shaped extremity. 



Hancock describes the peduncle as composed of a dense, muscular, semi-cartilaginous 



1 Article " Terebratula," in the ' Dictionnaire des Sc. Naturelles,' torn. 53, p. 132, 1824. 



- " Ueber das Oeffnen and Schliessen der Brachiopoden," Wiegmann's 'Arch.,' vol. ii, pp. 220, 222, 

 pi. iv, figs. 4, 5, 6, 1835; see also Davidson, ' Annals and Mag. of Nat. Hist.,' December, 1855, where a 

 translation of Quenstedt's paper is given. 



