ANIMALS. 73 



of corresponding size of the same species exhibit any trace of this structure.^ As 

 already observed, the foraminated deltidium of Orthisina adscendens does not appear to 

 be general in the species. It will thus be understood, that I am little disposed to agree 

 with M. Alcide d'Orbigny^ in making the foramen in StrophomenidcB a generic character. 



Most of the palliobranchiate genera are furnished with a prominency, more or less 

 developed, in the centre of the hinge of the small or imperforate valve (PI. VI, fig. 

 45^; PL VIII, figs. 3, 5f/; PI. XI, figs. 10a, 11, 12; PI. XIX, fig. 3a; PI. XX, 

 fig. 7 e). This boss, as in future it will be termed, exists under various forms in 

 difi"erent genera ; it is very small in Cleiothpis pectinifera (Pi. X, fig. 9 c) ; rounded, 

 and a trifle larger in Camerophoria midtiplicata ; about the same size, and cup-shaped 

 in Waldheimia Australis (PI. XX, fig. 11/); larger, and bisected in L€p)t(B7ia analoga 

 (PI. XX, fig. 7 <?) ; still larger, and bi- or trilobed in Produdus horridus, (vide PI. XI, 

 figs. 1], 12), and some other genera; elongated, and somewhat erect in Orthis eximia,^ 

 and some species belonging to the Cretaceous system ; and drawn out, assuming a 

 nearly horizontal position on a thick cardinal plate in Bouchardia rosea. In 

 Trigonotreta undulata (PI. IX, fig. 7 h), Hypothyris psittacea, and many other shells, 

 the boss does not exist ; while, on the other hand, it is enormously developed in 

 Striyocephalus Burtini (PI. XIX, fig. 1 e), forming a massive, curving process, stretching 

 from the hinge to nearly the centre of the opposite or large valve, where it clasps, as it 

 were, the ventral median plate by means of its dilated bifurcated extremity. These 

 modifications will show that the boss has not served as a tooth or an articulating instru- 

 ment, as is generally considered ; the cavities (sockets) on each side of it, and their 

 occupying parts, were the only structures adapted for this purpose. As will after- 

 wards be shown, the boss served as a fulcrum for certain muscles ; but it may be 

 observed, in the present place, that its non-articulating character is clearly proved b}' 

 the markings usually displayed on its surface in Productus (PI. XI, fig. 11) dind Leptana 

 (PI. XX, fig. 7 e), and by the complete absence in the hinge of the opposite valve of a 

 correspondingly marked depression in which it could act. 



The muscular system of the Palliobranchs may now be described. With perhaps 

 but few exceptions, the umbonal cavity of a brachiopod shell is furnished with a 

 dense, fibrous, cylindrical body, termed the pedicle. In Waldheimia Australis the inferior 

 end of the pedicle fits into the foramen (PI. XX, fig. 12 a), and its superior end, 

 which is somewhat flattened or dilated in the transverse direction of the shell, is 

 situated at the entrance or anterior part of the rostral cavity, to the surface of which 

 it appears to be attached by means of tendinous or membranous chords ; the truncated 

 extremity of the pedicle itself apparently not being adherent. There is one genus, 



1 Mr. D. Sharpe has found a " foramen in some young specimens" of the same shell from the Wenlock 

 Slate. (Vide Quarterly Journal of the Geol. Soc., vol. iv, p. 1/2.) 

 '■^ Comptes-rendus de I'Acad. des So., vol. xxxvi, 5 Aout, 1847. 

 ^ Geology of Russia, vol. ii, p. 192, pi. xi, fig. 2 e. 



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