8 INTRODUCTION. 



the swollen part of the capsule of the peduncle, penetrate the capsule, interlace with the 

 inserted fibres of the inferior retractor, and terminate for the most part in the peduncle. 



Some not very clearly defined, partly carneous, chiefly tendinous, fibres, which 

 interlace, running mostly in the transverse direction upon and in the capsule of the peduncle, 

 and make up, in fact, a chief part of its substance, have a transversely oblong surface of 

 attachment or strong adhesion to the lower part of the bent conical prolongation of the 

 ventral valve lodging the peduncle : this surface appears in the exterior of the soft parts 

 of the Terebratula, behind the origins of the cardinales muscles, fig. 2, p. 9, /. I have 

 proposed the name of ' capsularis,' for the sum of the carneo-tendinous fibres which have 

 the attachment in question. In conjunction with the completely encircling fibres of the 

 peduncular capsule, they must compress and elongate the peduncle. 



In addition to the carneo-tendinous fibres arranged in the more or less definite masses 



above-described, there must be enumerated in the muscular system the double spiral fibres 



which form the muscular wall of the canal, pi. i, fig. 1, and pi. iii, fig. 2, z, traversing the 



stems of the fringed arms; and the muscular fibres of the pallial lobes, which latter 



are extremely feebly developed, and recognisable only near the periphery. Thus, to 



recapitulate the designations of the several muscles in the Terebratula, as demonstrated 



by dissections of the Ter, chilensis, Ter. psittacea, and Ter. Jlavescens, there may be 



enumerated the — 



Adductor longii,s anticus. 



Adductor lonc/us posticus, 



Adductor brevis, 



Cardinalis, 



Betractor superior. 



Retractor inferior, 



Capsularis, 



Brachial muscles, 



Ballial muscles. 



The first seven muscles leave more or less recognisable impressions on the interior 

 of the valves : the marginal muscles of the mantle are too feebly developed to mark the 

 shell, as it is impressed in the Lamellibranchiate bivalves.^ 



In the subjoined cuts the muscular impressions and some other parts of the valves are 

 indicated by the following letters : — Fig. 1 (Dorsal Valve) : a, cardinal or hinge-process ; 

 h, depression for hinge-teeth ; c, hinge-plate ; e, crus or origin of calcareous loop ; 

 e', crural process ; /, produced plate — g, reflected plate — of calcareous loop ; d, impression 

 of adductor longus anticus ; p', impression of adductor longus posticus. Fig. 2 (Ventral 



1 Most of the above details of the muscular system were communicated by me to the Meeting of the 

 Italian naturalists at Naples in 1846; and an abstract was left for publication in the 'Annals' of that 

 Meeting. 



