ANATOMY OF THE TEREBRATULA. 



Valve) : i, perforation for passage of peduncle ; k, accessory shelly piece, called ' thecidium;' 

 /, hinge-tooth ; q', impression of adductor brevis ; s, impression of adductor inferior ; 

 o\ impression of confluent attachments of the adductores longi ; u, impressions of the 

 cardinales or hinge-muscles ; /, impression of the capsularis ; ■^, the position of the anus. 



Fig. 1. 



Fig. 2. 



Inner surface, with calcareous loop, and muscular impressions 

 of the Dorsal Valve, Terebratulaflavescens, (magn.) 



Inner surface and muscular impressions of the Ventral 

 Valve, Terebratula flavescens, (magn.) 



With respect to the fringed arms, I have very little to add to the descriptions in my 

 earlier Memoir. The modifications of the calcareous support — a kind of internal skeleton, 

 fig. 1, p. 9, and pi. 1, fig. 2, — have been fully and accurately detailed by my able colleague, 

 Mr, Davidson, in his communications to the ' Annals and Magazine of Natural History,' 

 and in the Monograph to which the present notes are prefixed. I shall only, therefore, 

 append some remarks on the arrangement of the soft parts supported by the calcified loop, 

 as they exist in the Terebratula flavescens. In this, as in other Terebratulce, the fringed 

 portions of the arms are not immediately supported by the loop, this serves only for the 

 attachment of the thin but firm aponeurotic membrane which forms the true basis of 

 support of the beautiful and peculiar organs in question. 



The crura, e, fig. 1, of the shelly-loop, are attached to the hinge-plates of the dorsal valve : 

 from each crus is continued a produced and a reflected plate, which latter are united by a 

 transverse portion completing the loop : a short descending process, e', is sent ofi" near the 

 basal attachment of each crus. The produced plate, /, pi. 1, fig. 2, after advancing 

 forwards to about three fourths of the antero-posterior diameter of the shell, bends towards 

 the ventral valve to form the reflected plate, g, and both portions are also bent with their 

 convexities outwards. The brachial aponeurosis, v, pi. 3, figs, ii and iii, which incloses the 

 loop and its processes, is continued transversely from one crus to the other, near the 

 hinge, forming the ' basal fold,' w, pi. 2, fig. i ; passes from the produced to the reflected 

 plates, binding them closely together, and forming the * lateral folds,' a, a, pi. 3, fig. iii ; 



2 



