127 



some elasticity, and when acted on by the museles becomes in its 

 reflected part sufficiently convex to press upon the perforated 

 valve and separate k sligluly from the opposite one ; thus compen- 

 sating for the absence of the thick arms o f Lingu la, which in their 

 protrusion push open the valves, and also for that of the elastic 

 fibres constituting the ligament of ordinary Bivalves. 



The Orbiculce examined by Mr. Owen consist of specimens of Orb. 

 lamellosa, Brod. 



Along the whole circumference of the valves shining cilia are 

 seen projecting for an extent varying from 2 to 4 lines : the}' are 

 consequentlymuch longer than in 2'erehratula and in Lingula unntina, 

 and are rather longer than in Ling. Audebardii, Brod. On exami- 

 nation under a high power they are observed to be beset vvith 

 smaller setce, which probably gives them greater power in determi- 

 ning the respiratory currents. The mantle is similarly vaseular to that 

 of Tcj-ebratula, theie being, in the upper lobe, four principai trunks 

 (comparatively, hovv'ever, much shorter than in that genus); and 

 two in the lower. These trunks terminate in sinuses, situated close 

 to two strong tendinous membranes, which circumscribe the visceral 

 mass, and to which the mantle-lobes firmly adhere. Herethe veins 

 of both mantle-lobes join, and the common trunk or sinus passesob- 

 liquely through the membrane, and maybe plainly seen distributing 

 ramuli over the liver and ovarj'. 



The museles and viscera form a rounded mass, situated in the pos- 

 terior half of the shell. The mouth is seated betvveen the base of 

 the arms. The cesophagus passes obliquely through the tendinous 

 \vall of the viscera in a direetion towards the upper valve : it be- 

 comes slightly dilated, and is then surrounded by the liver. The in- 

 testine is continued straight to the opposite end of the visceral ca- 

 vity, is there again contraeted, makes a sudden bend upon itself, 

 and returns to the middle of the right side of the visceral beit, which 

 it perforates obliquely, and terminates between the lobes of the 

 mantle a little below the bend of the arm. The liver is of a beau- 

 tiful green eolour, and consists of a congeries of elongated fol- 

 licles, closely compacted together, which communicate by numer- 

 ous orifices with the stomach. As in Terebratula, there is no sali- 

 vary gi and. 



In Lingula Audebardii, Brod., there is also no salivary gland; and 

 Mr. Owen is therefore disposed to believe that the gland described 

 as sueh in Ling. anatina by Cuvier, was only a portion of the liver, 

 from which the čolour had probably been removed by long macera- 

 tion in spirit. 



In the want of salivary glands the Brachiopoda would agree with 

 the ordinary Bivalves. Destitute, likę them, of apy hard parts about 

 the mouth for comminuting alimentary substances, glands for 

 pouring in a fluid to blend vvith the food during that operation are 

 not wanted. 



The nervous system in Terebratula was not detected by Mr. 

 Ovven. In Orbicula tvvo small ^awg^/a werefound on the side of the 

 cesophagus next the perforated valve ; from which two filaments, ac- 

 companying the cesophagus through the membranous wall, imme- 

 diately diverge and pass exterior to the anterior shell museles^ pro- 



