Mr. T. Davidson on the Brachiopoda. 445 



EXPLANATION OF PLATE X. 



Fig. 1 . Waldheimia septigera, Loven, sp. 



Fig. 2. cranium, Miiller, sp. 



Fig. 3. Terebratella Spitzbergensis, Dav. 



Fig. 4. Magas (Rhynchora) Davidsoni, De Koninck, sp. Interior of the 

 dorsal or smaller valve, from drawings by M. Bosquet of Maes- 

 tricht. 4 a, longitudinal section of both valves ; p, pedicle mus- 

 cular impressions ; t, sockets. 

 Fig. 5. Waldheimia australis, muscular system, from an improved diagram 

 prepared by Mr- Hancock. 

 A. Adductor {adductores longi, Owen), attached to the ventral 



valve. 

 A'. PLAAwciOY {adductor longus posticus, Owen. Muscle adducteur 



principal, Gratiolet). 

 A". Adductor [adductor longus anticus, Owen. Muscle adducteur 



principal, Gratiolet). 

 R. Cardinal muscle {adductor brevis, Owen. Muscles diducteurs 



principaux, Gratiolet). 

 R'. Accessory cardinal mviscle {cardinales, Owen. Muscles diduc- 

 teurs accessoires, Gratiolet). 

 P. Ventral pedicle muscles {retractor inferior, Owen. Muscles du 



pedoncule paire superieure, Gratiolet). 

 P'. Dorsal pedicle muscles {retractor superior, Owen. Muscles du 



pedoncule paire inferieure, Gratiolet). 

 P". Pedicle sheath. 



Z. Capsular muscle {capsularis, Owen). 



M', mouth ; i, intestine ; L, loop ; L", reflected portion of the same. 



Fig. 6. Dorsal valve of a Terebratula : a, the sockets ; b, the opening 



muscles ; c ^ d, the muscular impressions. (Figs. 6, 7 & 8 are 



taken from Prof. Quenstedt's paper.) 



Fig. 7' Ventral valve of the same Terebratula : a, the lateral teeth ; b, the 



muscular impressions ; c Sf d, the two bundles of the closing 



muscle (adductor). The letters correspond to those in fig. 6, so 



that by the inspection of the following one — 



Fig. 8. seen in profile — the mechanism of the opiening and closing of the 



valves may be easily understood. 

 Fig. 9. The male sexual glands of a Terebratula. Figs. 9, 10, II, 12, 13 



& 14 are taken from Prof. Schmidt's paper. 

 Fig. 10. Spermatozoa of the same. 

 Fig. 11. Embryo of the same Terebratula, magnified. 

 Figs. 12, 13 & 14. Calcareous structure (or plates) from the mantle and 



brachial cirri of Terebratulina caput-serpentis. 

 Fig. 15. Embryos removed from the ovarian cavity in the pallial sinus of 



Lingula anatina : magnified 120 diameters (Owen). 

 Fig.\&. Rhynchonella Gray i (Woodward). 16 c, enlarged. 



Fig. 17. psittacea. 



Fig. 18. nigricans; these are the only three recent Rhynchonellce at 



present known. 

 Fig. 19. Morrisia anomioides, Scacchi, sp. 19«, enlarged. 

 Fig. 20. Morrisia Davidsoni, E. Deslongchamps. 20 a, b, enlarged. 

 20 c, d, enlarged views of the interior of the smaller or dorsal 

 valve, part of the lamellae being broken off ; /, foramen ; t, sockets ; 

 M, departure of the crural lamellae ; n, broken lamellae attached 

 to the summit of the septum, s. 



