belonging to the Class Palliobranchiata. 41 



The whole of the impressions noticed in the last paragraph are 

 best seen in certain Froductuses. The two large striated im- 

 pressions on the convex valve of Productus giganteus I have satis- 

 tied myself are due to the superior pedicle muscles*. Within 

 these, and on a flattened elevation, are situated four other im- 

 pressions curiously ramified ; they are often confluent, but occa- 

 sionally specimens exhibit them separated. Two of these im- 

 pressions (probably those situated anteriorly) I consider are due 

 to the valvulars, and the other to the cardinals : the former 

 muscles, according to this view, have necessarily produced the 

 ramified impressions generally to be seen on the flat or opposite 

 valve f. The tubercle on the centre of the hinge of the flat valve 

 has commonly been considered a tooth, but the impressions which 

 it displays, and its agreement in position with the cardinal pro- 

 minency of Terebratula dorsata, prove that it served as a muscular 

 fulcrum, and there is every reason to suppose that the cardinal 

 muscles were attached to it J. M. Bouchard Chantereaux appears 



* The use of the so-called pedicle seems to be twofold — to moor the shell 

 to foreign bodies, and to serve as a fulcrum for certain muscles. In the 

 Strophomenas and Leptaenas generally, owing to the deltidium being cica- 

 trized, or occupied by the base of the cardinal tubercle, the pedicle can only 

 have been used for the latter purpose ; in S. alternata, L. analoga, &c, 

 which have a foramen, it would answer both. The same remark applies to 

 the Orthises (O. anomala) and Spirifers OS", heteroclitus, &c.) : as the del- 

 tidium is often open in the last genus, it appears to have served as a passage 

 for the pedicle. From the closing of the foramen in old individuals of many 

 species of Terebratula (T. variabilis, T. carnea, &c), Leptcsna (L. analoga), 

 H'fpothyris and other genera, it is evident that the pedicle was occasionally 

 dispensed with in old age. In young Strigocephaluses the pedicle passed 

 through an open deltidium, as in many Spirifers ; in individuals more ad- 

 vanced it passed through a circular aperture in the cicatrix of the deltidium 

 (in which case it is an "entire, subapical foramen," resembling that of many 

 Hypothyrises) ; in full-grown individuals the pedicle was dispensed with, as 

 the deltidium is completely cicatrized. M. Verneuil informs me that the del- 

 tidium is exposed and open in young specimens of Penlarnerus Knightii', it 

 is well known to be concealed in old ones : in another species of the same 

 genus (P. conc/iidium) it is exposed and open. It will thus be evident, al- 

 though neither foramen nor deltidium is to be seen in Productus, that this 

 is no evidence of its having been without a pedicle mass. 



f The ramified impressions on the two valves of Productus are generally 

 considered to have been produced by the viscera ; nor was it until lately, 

 and after seeing that the fibres of the muscles of Terebratula dorsata had a 

 ramified arrangement, that I could be induced to think otherwise. The 

 stopper muscle of certain species of Anomia produce a similar ramified im- 

 pression on the upper valve. 



\ M. Verneuil, speaking of Productus, says, " La valve ventrale possede 

 line forte dent mediane, quelquefois simple, plus souvent bifurquee ou tri- 

 furquee a, son extremite, et representant les deux ou trois dents des Orthis 

 et des Leptcena re'unies et soudees ensemble." (Geology of Russia, vol. ii. 

 p. 251.) This so-called tooth, with its bipartite or tripartite extremity, I 

 have never seen fitting into a correspondingly divided depression ; therefore, 

 irrespectively of the counter-evidence given in the text, this fact alone is suf- 

 ficient to prove that it is not an articulating instrument. 



