46 DR. T. DAVIDSON ON RECENT BRACHIOPODA. 



peduncle to the shell, and thus controlling the steadying of it upon the peduncle. These 

 details and the figure taken from Hancock will sufficiently explain the functions of the 

 different muscles. Hancock describes the peduncle as composed of a dense muscular, 

 semi-cai'tilaginous mass of a cylindrical form. 



The nature of the muscles has also been well described and illustrated by Owen, 

 Gratiolet, and more recently by Van Bemmelen, in his anatomical memoir ' On the 

 Structure of the Shells of Brachiopods and Chitons ' *. 



Owing to the strong and tiglit interlocking of the valves of Waldhelmia flavescens and 

 other species, by means of curved teeth and sockets, the Brachiopoda would seem to open 

 their valves very slightly. 



At p. 806 of the admirable memoir already alluded to, Hancock says that in Waldlieimia 

 flavescens and in other forms of the genus, the " loop originates in the hinge-plate in 

 two necks or processes, — the crvira, from which two jioints project downwards, called the 

 crural processes. The upper or dorsal members of the loop, passing from these two 

 lateral necks, stretch forward for about two thirds the length of the valve, then bend 

 towards the ventral valve, and turning back upon their course, are united across the 

 median line, a short way in advance of the crural processes. The lateral portions of 

 the loop are curved a little outwards. The whole of this calcareous support, in- 

 cluding the crura and crural processes, is a product of the inner lamina of the dorsal 

 pallial lolje. This lamina, with the exception of a portion at each side, which is con- 

 tinuous with the similar lamina of the ventral lobe, forming with it the anterior wall of 

 the perivisceral chamber, is turned downwards and forwards, and extends as far as the 

 transverse portion of the loop. It then divides into two lobules, one passing to the 

 anterior extremity of each of the lateral portions of this calcareous support, binding 

 together the dorsal and ventral members. The loop in its sinuous course follows tlie 

 margins of this bifurcated pallial process, and lies imbedded in its substance. 



" The arms themselves taper to fine jioints, having taken their origin at each side of the 

 mouth, which is situated at the back of the pallial chamber in a central position, opening 

 downwards. They pass outwards and forwards in connection with the calcareous loop and 

 the pallial lobules, running along the outer edge of the dorsal member of the former ; 

 they then turn back upon the reflected or ventral part of it, and on reaching the trans- 

 verse portion bend inwards and doubling sharply upon themselves, again advance and 

 go to form two vertical spirals turned towards the dorsal valve. The spirals are placed 

 parallel to each other, and throughout the coil, consisting of two or three turns, they 

 are united across the median line by a rather wide, stout, semicartilaginous membrane, 

 which is attached behind the transverse portion of the loop." 



The labial appendages have been magnificently illustrated by Owen in plates 1 & 2 

 of his chapter on the ' Anatomy of the Terehratula ' already referred to. They are also 

 minutely described and illustrated by Gratiolet in his ' Etudes anatomiques sur la 

 Terebratule australe,' 1857. 



These appendages are, in TF'aldheimia flavescens, as well as in other species of the 



* ' Over den Bouw der Schclpcn van Brachiopodeii en Chitonen,' Leiden, 18S2, and of which an English note will be 

 found in the Ann. & Mag. Nat. Hist. 5th ser. vol. xi. p. '37Q, 1S83. 



