8 Prof. W. King on some 



The various muscles, including the parietals, produce scars, 

 often well seen in the valves of recent Lingulas. The scars 

 are occasionally liable to become raised at their margin, giving 

 them the appearance of individualized muscular fulcra or myo- 

 phores. A specimen before me has the scar of one of the post- 

 latcro-parietals with its inner margin completely raised in the 

 form of a plate. Such cases are evidently of abnormal forma- 

 tion ; but they explain the origin of what may be assumed as 

 normal cases — for example, Lingula aJbiJa^, in which there 

 are two of the same kind of plates. The attachments of the 

 gastro-parietal bands })roduec in the dorsal valve two transverse 

 impressions (corresponding to <),each of which passes behind one 

 of the central muscle-scars, with a slight undulation, to nearly 

 the middle line of the shell. In Lejytama anaJoga the myophore 

 of the dorsal valve has a transverse laminar division, inter- 

 rupted in the middle, which might be taken for the fulcrum of 

 the gastro-parietal bands f ; but this view could only be correct 

 if the muscle-scars in the fossil referred to were, as in 

 Lingula^ situated in front of the laminar division, which is not 

 the case. 



As the shell-muscles of Lingula differ so widely from those 

 characterizing most Palliobranchs, it cannot be expected that 

 many fossils of the kind should exhibit scars indicating their 

 possession of a similar myology. The remains of extinct 

 species of Lingula occasionally show the characteristic scars, 

 as may be seen by referring to Mr. Davidson's figure of 

 Lingula Leivisii \. In this species, however, the central 

 muscles appear to be situated much further back than in L. 

 anatina. So far my researches have failed in detecting in 

 fossil Palliobranchs any scars that have been produced by 

 muscles homologous with the transmediaus of Linqula. 



igi 



In comparison with the splanchnocojle of the Terebratulids 

 and other shells allied to them, that oi Lingula is not only more 

 voluminous, but it has much thicker walls. In the former the 

 parietals, being membranous and extremely thin §, leave little 



* GlottidUi ulbida of Uall (see 'American Journal of Conchology,' vol. vi. 

 p. 157, pi. viii. fig:. -2). 



t Kiu^, ' Monof^raph of Permian Fossils,' pi. xx. fig. 7. 



X British Silurian Bracliiopoda, pi. iii. figs. 5 & 6. 



§ The membranous parietals in the Terebratulids are occasionally 

 strengthened by calcareous plates, so much so in 'Terebratulina caput- 

 serpc-uHs that they are crowded and beautifidly tessellated with radial 

 forms of the latter, as is also the case in the exposed or outer layer of 

 the mantle where it covers the ovaries. It would therefore not surprise 

 me to find that in some fossil species the visceral organs had been more 

 or less protected by completely calcified parietes. My colleague and self, 

 it is probable, may succeed in showing that the curious internal structures 

 occurring in the typical Trimerellas served as receptacles for certain 

 viscera. 



