44 DE. T. DAVIDSON ON KECENT BRACHIOPODA. 



The loop passes likewise through a series of metamorphoses from the very young 

 state up to the period when it assumes the simple adult Tfaldheinda-chareicter, as has 

 been so elaborately described and illustrated by Herman Friele in the case of TFald- 

 heimia septlgera and Wcddheimia (or Macandrevia) cranium. 



The intimate shell-structure of JValdheimia ficwescens has been minutely described and 

 admirably illustrated by Dr. W. B. Carpenter, in his chapter " On the Intimate Structure 

 of the Shells of the Brachiopoda," which he kindly prepared in 1853 for vol. i. of my 

 ' Monograph on British Fossil Brachiopoda,' and to which the reader is referred. But we 

 may here mention that he found the perforations in 7?^. jiavescens to average a diameter 

 of about 8^0 inch, and the distance of their centres about j^. Three of his illus- 

 trations have been given in PI. VII. figs. 17-19. 



In 1869, in vol. xxiv. of the Transactions of the Royal Irish Academy, Prof. W. King 

 gave an excellent description of the shell-structure of the species under description, in 

 which he observes that Quekett, in 1850, discovered that the extremity of the caecal 

 appendages, as they are now^ generally called, is more or less flattened or disk-shaped, and 

 encircled with a fringe of exceedingly minute radiating lines or membranous filaments. 

 Prof. King adds, " In position and arrangement the ^laments belonging to the termina- 

 tions of the ca?cal appendages so completely agree with the radiating lines which intersect 

 the apertural rims of the perforations, as to leave no doubt on my mind that the latter 

 are tubular and enclose the former." The shell of JF. Jiavescens and its intimate shell- 

 structure is also described by Gratiolet, in his admirable memoir " Etudes anatomiques 

 sur la Terebratule australe," Journal de Conchyliologie, 1857. He says, at p. 214 of his 

 memoir, that the shell, when divested of the foreign objects that generally cover its 

 surface, is of a tolerable transparency. One notices in it, besides the concentric lines of 

 growth, diverging costae which give to the sharp edge of the valves an undulated appear- 

 ance ; examined with a lens, its surface is finely granulous, so much so, that one might 

 think it formed of veiy fine granulations ; but this aj)parent granulation is due to a 

 multitude of microscopic perforations with Avhich the shell is riddled. These perforations 

 are, besides, very irregularly disposed on parallel bands which intercept quadrilateral 

 spaces. He adds that the substance of the shell is formed of small calcareous prisms, 

 somewhat attenuated at their extremity and disposed in parallel layers, which give 

 to the fractured shell a fibrous aspect ; these elements are closer together towards the 

 edges of the shell than in their central poi'tions. 



The soft parts of the animal of Waldheimia Jiavescens have been admirably described 

 and elaborately illustrated by several eminent anatomists. First by Owen in 1853, in 

 the Introduction to vol. i. of my work on ' British Fossil Brachiopoda ; ' subsequently, 

 in 1857, by Pierre Gratiolet, in his memoir above quoted, and in the following year by 

 Albany Hancock, in his classical memoir " On the Organization of the Brachiopoda " 

 (Phil. Trans. Boy. Soc. vol. cxlviii.). To these works the reader is referred for more 

 complete anatomical details than we are able to reproduce in this monograph. 



The body proper is small when compared with the size of the shell, and has both its 

 valves lined by a delicate bilobed integument or membrane, termed the ' pallium ' or 

 mantle ; this secretes the shell and is fringed with horny bristles. The mantle is composed 



