BRACH10P ODA. 
55 
occasionally manifested in both valves of the species to form two or three 
vaults on either side of the platform. In animals of the size indicated by these 
shells the lobation of the liver may have been so strongly developed as to pro¬ 
duce this peculiar effect in the excavation of these cavities. Admitting the 
sequestration of the liver in Trimerella, a freer play would undoubtedly be 
left to the muscles and greater opportunities of development, and this fact will 
have had both a direct and inverse bearing on the size attained by both the 
platform and the shell itself. 
In regard to the great umbonal chambers of the pedicle-valve in Monomer- 
ella, and their lesser development in Dinobolus and Trimerella, they have pos¬ 
sibly served a similar function to the platform-vaults, by removing the delicate 
genital organs from dangers which might arise from the action of the muscles. 
In Lingula anatina, these organs lie normally in the median and posterior portion 
of the visceral region, pressing backward against the post-parietal wall, and are 
placed mostly on the ventral side of the body. In offering an interpretation 
of the arched posterior scar in Lingulops, Davidson and King suggested that the 
middle sinus of the arch might have been produced by the umbonal muscle 
pressing against the parietal wall, and the lateral sinuses have been due to the 
pressure of the ovarian lobes against this muscular wall. Were this the case 
in the genus where all these features are in an initial stage of development, it 
would readily be conceived how by this constant pressure the genital organs 
may have developed the umbonal cavities for their own protection. 
Genus LINGULELLA, Salter. 1866. 
PLATE II, FIGS. 1-13. 
1852. Lingula, McCoy. Annals and Magazine of Natural History, Second Series, vol. viii, p. 405. 
1852. Lingula, McCoy. British Palseozoic Fossils, p. 252, pi. 1 l. 
1859. Lingula, Salter In Murchison’s Siluria, Fourth Edition, p. 43. 
1866. Lingulella, Salter. Mem. Geological Survey of Great Britain, vol. iii, p. 333. 
1866. Lingulella, Davidson. British Silurian Brachiopoda, p. 55. 
1867. Lingulella, Salter. Quarterly Journal Geological Society, p. 340. 
1868. Lingulella, Davidson. Geological Magazine, p. 303. 
1871. Lingulella, Davidson. British Silurian Brachiopoda, p. 336. 
