DE. T. DAVIDSON OX EECENT BEACIIIOPODA. 67 



convex longitudinally, slig-litly flattened along the middle. Ventral valve deeper and 

 more convex than the dorsal one, without sinus ; beak incurved, truncated by an 

 incomplete foramen, margined laterally by small deltidial plates. In the interior of the 

 dorsal valve the loop is long and simple, the principal branches extending to a little 

 beyond two thii'ds of their length before becoming reflected. Length 9, width 7, depth 

 5 lines. 



Hah. Only one incomplete example was dredged by the 'Challenger' Expedition, off 

 Valparaiso, at a depth of 21C0 fathoms. Terchratida Wi/vlllii and Discinisca atlantica 

 were obtained at the same time. 



Ohs. In external shape this species approaches Waldheimia cranium, which is, however, 

 a thicker and more convex shell. The extremely delicate shell of W. Wyvtllil is very 

 remarkable, and reminds us of that of W. tenera, from which, however, it seems to 

 differ in size and in some other particulars. 



The fact that several of the species obtained at such depths as Terehralula Wyv'dlii 

 and Discinisca atlantica possess such extremely thin and delicate glass-like shells, is 

 certainly worthy of notice. 



Note. — In accordance with the verbally expressed wishes of the late Thomas Davidson, LL.D., 

 F.R.S., " The Davidson Collections of Recent and Fossil Brachiopoda" were presented to the nation, 

 with the manuscripts and original drawings for many of his publications on the Brachiopoda, and the 

 extensive sci-ics of works and pamphlets he had accumulated during nearly fifty years' investigation of 

 this group of animals. The recent specimens are associated with the fossil species in the Geological 

 Department of the Natural History Branch of the British Museum at South Kensington. The literature 

 now forms part of the libraiy of the same department in that Institution. [A. C] 



DESCRIPTION OE THE PLATES. 

 Plate I. 



Figs. 1-6. Liothyris vilrea, Born, sp., at various stages of growth. Mediterranean Sea (Davidson 

 Collection, Geological Department, British jNIuscum). G. Interior of the dorsal valve, 

 enlarged, cp, cardinal process ; si, short loop ; clg, diverging grooves for the attachment of the 

 pallial sinuses. 



Fig. 7. Exterior of ventral valve of the same species, showing the four internal radiating furrows which 

 serve for the attachment of the pallial sinuses, seen tlirough the transparent shell. 



Fig. 8. Interior of the ventral valve after E. Ueslongchamps. cv, visceral cavity ; ap, raised portion of the 

 mantle forming the walls of the visceral cavity ; svl, furrow corresponding to the lateral 

 venous sinus ; svm, furrow corresponding to the median venous sinus. 



Fig. 9. Interior of the ventral valve showing the position of the muscular impressions, a, adductor 

 or occlusor ; b, ventral adjustors ; c, divaricators. 



Fig. 10. Malformation of Liothyris viirea (after E. Deslongchamps) , seen in profile, showing a longitu- 

 dinal frontal septum in both valves. 



Fig. 11. Full-grown spieulum, much magnified (after E. Deslongchamps), from a venous sinus near the 

 raised part of the mautle oi Liothyris vitrea. 



Fig. 12. Portion of the shell of Liothyris vitrea, magnified (after Van Bemmclcu), to show the perforations 

 and imbricated arrangement of the prisms. 



9* 



