74 PERMIAN FOSSILS. 



Productus, which, on account of its never displaying either a foramen or fissure, might 

 be supposed to be unprovided with a pedicle ; but as this part, as will shortly be seen, 

 affords attachment to several muscles, it seems unsafe to predicate its absence in any 

 palliobranchiate genus whatever, but particularly in one intimately related to forms 

 (e. g. Strophomena and Leptana) which undoubtedly possessed it. 



The pedicle may be said to serve two purposes : first, the mooring of the 

 shell to foreign bodies ; and, second, as a muscular fulcrum. In the imperforate 

 Strophomenas and Leptsenas it can only have occupied the latter office, since the 

 fissure is either closed with a deltidium, or completely filled up with the boss of the 

 opposite valve ; but in the perforated species, as Strophomena alternata, Leptcena analoga, 

 &c., it is clear that the pedicle has served both purposes. The simple office, that is, 

 its answering as a base of attachment for certain muscles, is the one I propose 

 assigning to the pedicle of Productus. The same simple subserviency of the pedicle is 

 evidenced in the non-foraminated Orthisinas {0. plana, 0. hemipronites) and Stropho- 

 menas {S. rugosa = (J) planumdona) ; while it is duplicated in such congeneric species 

 as Strophomena alternata and Orthisina Verneuili. From the foramen becoming closed in 

 old shells, it must be concluded- that the pedicle, as a mooring instrument, was dispensed 

 with in old age : my large specimens of Leptcena analoga show the foramen distinctly 

 closed. In young examples of Strigocephalus Burtini the pedicle passed through an 

 open fissure, as in many Spiriferidias ; in individuals of a more advanced age, it passed 

 through a foramen in the deltidium, which had gradually filled up the fissure ; while 

 in those full grown, it was dispensed with, as proved by the filling up of the foramen 

 as well. 



In the perforate valve of Waldheimia Australis three pairs of muscles pass from the 

 inside, a little in advance of the upper end of the pedicle, to different situations. The 

 outermost pair, which consists of the muscles implanted nearest the sides of the 

 valve, passes at a slight angle into the upper part of the pedicle (PI. XX, figs. 10, 

 12 b). Within these muscles, and somewhat in front of them, another pair 

 (PI. XX, figs. 10, 12 c) passes downwards, slightly converging at the same time, 

 and becomes attached to the boss on the hinge of the imperforate valve (PI. XX, 

 figs. 11, 12/). To distinguish these two pairs of muscles from each other, it is 

 proposed to name the former the superior piedicle muscles, and the latter the cardinal 

 muscles. 



A little in front of the superior end of the pedicle, and a little behind and within 

 the attachment of the cardinal muscles, and therefore near the medio-longitudinal line 

 of the perforate valve, is implanted the remaining pair, which passes directly down to 

 a little behind the centre of the imperforate valve ; each muscle, at the same time, 

 becoming dichotomous in its inferior half (PI. XX, figs. 10, 12^): these may be 

 termed the valvular muscles. In addition to the cardinals and the valvulars, the 

 imperforate valve affords attachment to other two muscles, which pass upwards from 



