22 PALAEONTOLOGY OF NEW YORK. 



however, there is a distinct development of the septum in this anterior portion 

 of the sliell, such as is also to be found in both valves of some Trimerellas. 



The posterior outline of the muscular region in the pedicle-valve is very 

 striking. It consists of a central lobe or scallop, at each side of which is a 

 somewhat broader lobe, continuous with the faintly defined lateral muscular 

 scar. It seems evident that this lobed impression, which has been aptly 

 compared, by Davidson and King, to a Moorish arch, is of muscular origin 

 and made by separate muscular bands. This appears from the fact that we 

 shall have to consider the crescent as the base of attachment of the parietal 

 walls. There is nothing, however, in Lingula or in the Trimerellids from 

 which an homology can here be satisfactorily elicited. While we should be in- 

 clined to regard the impression as entirely a muscular scar, we may quote the 

 remarks of the authors above referred to: 



" The middle sinus, we have little doubt, has been produced by the umbonal 

 muscle pressing against the post-parietal or posterior wall of the splanchnocoele. 

 It may be suggested that the lateral sinuses have been formed in the same way 

 by other muscles, but as Lingula is not characterized by any similarly situated 

 (at least in the brachial valve*), we prefer the idea that they represent certain 

 viscera; and they may be recesses produced by the pressure of the ovarian 

 lobes against the inner side of the post-lateral walls of the splanchnocoele '.' 

 (pp. 166, 167). 



The validity of this speculation apparently rests, to a great degree, upon the 

 conception of the authors, that the valve under consideration is not the pedicle- 



in the middle, due. we believe, as in Lingula, to this poi-tioii having been forced out by the pedicle ; while 

 the crescent in the brachial valve has a pointed crown directed backward ; now it is this peculiarity that 

 plainly presents itself in Limgblops." Ag-ain : " In the Trimerellids, as in Lingula, the pedicle-valve has 

 a short, rudimentary median plate, whereas in their brachial valves this part is well developed and elongated, 

 as it evidently is in Lingulops." Considerable importance is g-iven by the authoi-s to the discussion of the 

 character and function of what they have termed the " semicii'cular zone," which we regard as the broad 

 inner moiety of the cardinal area, more extremely developed in Mokomerella and Rhinobolds. The sugges- 

 tion is made that it is homologous with that area in the brachial val\-e of Lingula occupied by the setal band. 

 We have preferred to consider the original valve as the ventral oi' pedicle-valve, pai-tly on account of the 

 pedicle-groove, which is certainly better defined than it appeared to Messi's. Davidson and King, as well as 

 from incontrovertible evidence derived from the opposite valve, which at that time was unknown. 



*■" In i\\e. pedicle-valve oi Lingula anatina fhe transmedian muscles have their attachment similarly 

 situated. Were the fossil the same valve, we shauld have had little hesitation in refen-ing the lateral sinuses to 

 these muscles, notwithstanding their being single on one side and double on the othei' in Lisgvla." 



