DR. T. DAVIDSON OX EECENT BRACHIOPODA. 53 



2 up to 23 lines iu length. When young and up to nearly half its growtli the shell is 

 almost circular and broadest anteriorly, ta^jering at the beak, and nearly as wide as long ; 

 with age the shell becomes elongated and gibbous. 



I have carefully observed and drawn the modifications that take place in the shape of 

 the loop, of which I give some illustrations in Plate IX. figs. 11, 12, 13. My figures 

 agree well with tliose published by M. E. Dcslongchamps in his ' Etudes Crititjues ' above 

 quoted, and they do not diftur from those peculiar to other species of the genus. In a 

 specimen two lines in length the whole loop is small, not extending further than to 

 about half the length of the valve, its principal lamellae, as well as the reflected portion, 

 becoming attached to the extremity of the upper sides of a perpendicularly elevated 

 septum, as in Ilagasella. After a time the septum becomes less elevated, the principal 

 stems of the loop acquire greater length, and give ofi" at about half their length a 

 horizontal lamella, which is also fixed to the septum, as in Tcrehratella ; later on this 

 horizontal lamella detaches itself from the septum, the principal stems of the loop 

 become more separate, and the reflective portion assumes the appearance of that of a 

 fuU-grown Waldheimia. 



Waldheimia Icnticiilaris was well described and figured by Desliayes in 1841, and also 

 by G. B. Sowerby and L. Reeve. It has had the good fortune to preserve the same 

 specific name, although located iu the genera Terehratula, Waldheimia, and Neotliyris. 

 As observed by Reeve, in his ' Monogr. of Terehrahila,' " Were it not that the habitats of 

 this and the preceding species [Terebratiila {Waldheimia) glohosa'] are well authenticated, it 

 would be difficult to believe that there is any specific difference between them. This is 

 rather lighter [with an] inflated growth, and the colour is remarkable, but the characters 

 n other respects are the same in detail throughout. The foramen is probably as small 

 as in T. globosa ; in all the specimens of T. Icnticularis that I have seen it is more or less 

 eroded, according to the circumstances of its attachment. The loop is precisely the same 

 in both species." There are, however, differences between W. venosa and W. lenticularis 

 which must not be overlooked. In well-preserved specimens of the last-named shell the 

 foramen is small, iu fact much smaller than in W. venosa, and separated from the hinge- 

 line by a well-developed deltidium in two pieces, in this respect more nearly resembling 

 Laqneus californicus. The beak is more incvirved, and the dorsal valve more uniformly 

 convex. The colour is also very difi'erent in the two species. It is also a smaller shell. 



29. Waldheimia kerguelenensis, Davidson. (Plate X. figs. 7-17.) 



Waldheimia kerr/uelerms, Davidson, Proc. Roy. Soc. vol. xxvii. p. 437, 1878, and {IV. kerguelenensis) 

 Report on the IJrachiopoda, Voyage of H.M.S. ' Challenger/ Zool. vol. i. p. 40, pi. iii., 1880. 



Shell OA-ate, ventricose, longer than wide, light yellowish white, smooth. Dorsal valve 

 most convex near the umbo, a slight mesial depression commencing about the middle of 

 the valve extends to the front, and is more or less distinctly margined on either side by a 

 faint raised line or ridge ; front line slightly depressed or nearly straight. Ventral valve 

 rather more convex than the opposite one, and more or less distinctly keeled by the 

 presence of a wide, convex, but slightly raised fold, which corresponds with the depression 

 in the dorsal valve. Beak moderately produced and incurved, truncated by a small 



