﻿154 T. Davidson — What is a Brachio])od ? 



26. Bavidsonia Verneuilii (fossil). To show the great thickness of the ventral valve 



a, and its mode of attachment to submarine objects by a portion of the 

 substance of this valve, b. dorsal valve ; d. small free space left for the 

 animal. 



27. Produckis Llangollensis (fossil). Longitudinal section to show the great difference 



in thickness of the valves, a. ventral ; b. dorsal ; d. space left for animal. 



28. Slrophomena filosa (fossil). To show the smaU space left for the animal between 



the valves. 



29. Waldheimia Jiavescens. Enlarged section of shell (after King), o. thick cal- 



careous innermost division ; n. intermediate thin calcareous division ; m. outer 

 division of thin membrane ; e. f. canals traversing the calcareous layers 

 and n ; the lower half of the perforation being considerably smaller in 

 diameter than the upper one. 



30. Terehratiila bullata (fossil). Section of shell near the external surface and 



parallel to it, showing the remarkably large size and close proximity of the 

 perforations. 100 diameters. 



31. Waldheimia flaveseens or australis. Internal surface of the shell, showing the 



imbricated arrangement of the exti-emities of the prisms, which are seen 

 longitudinally at A, magnified 100 diameters. 



32. Vertical section, considerably enlarged, so as to show the ordinary 



ti'umpet-like form of the vertical passages and remarkable condition which 

 they exhibit in the inner and (probably) later-formed layer. 



33. Ehynchonella psittacea. Portion of the internal surface of the shell more highly 

 magnified, showing the imbricated arrangement and the entire absence of 

 perforations, magnified 100 diameters. 



34. Portion of the shell, showing at a the internal surface, with the 



imbricated arrangement of the extremities of its component prisms, and at 

 b the aspect of the prismatic substance as displayed by a fracture nearly in 

 the direction of the length of the prisms, showing also entire absence of 

 the least trace of perforations. Magnified 40 diameters. Figs. 30 to 34 

 after Dr. Carpenter. 



35. Lingula anatina. Longitudinal section of the shell to show the alternation of 



calcareous and horny layers ; b. b. calcareous layers perforated by miaute 

 canals ; d. d. horny layers. After Dr. Gratiolet. 



36. Crania anomala (enlarged). Interior of the dorsal valve to show the position of 



the spiral appendages. From a specimen m the Museum of the School 

 of Mines. 



FIG. CLISTENTERATA. PLATE VIII. 



1. Terebrattda carnea (fossil). Interior of the dorsal valve, to show the short 



simple loop. 



2. Terebratidina caput-serpentis. Interior of the dorsal valve, to show the ring- 



shaped loop. 



3. Magas pumilus (fossil). Longitudinal section to show the large central septum 



and disunited deflected portion of the loop. 



4. Bouchardia tulipa. Interior of the dorsal valve, to show the anchor-shaped 



apophysis. 



5. Thecidium mediterraneum. Seen ia profile. The valves opened as in life. After 



Lacaze-Duthiers. 



6. Spirifer Schrenkii (fossil). Interior of the dorsal valve, showing the cardinal 



process, quadruple impression of the adductor muscle, and one of the cal- 

 careous spiral laminffi for the support of the labial appendages. 



7. Atrypa reticularis (fossil). Interior of the dorsal valve, sho^ving the position 



and shape of the spiral laminte for the support of the labial appendages. 



8. One of the spiculse of the mantle of Terebratulina caput-serpentis highly mag. 



9. Rhynchonella psittacea (after Hancock) much enlarged. Dorsal view of the 



animal ; a. paUial lobe ; c. peduncle ; d. great pallial sinuses giving ofi' 

 branches at the margin; i. extremities of adductor muscle; n. liver; 

 X. spiral brachial apparatus ; s. genitalia and muscular ties uniting the 

 walls of the genital sinuses. 



10. Waldheimia australis (after Plancock). Diagram of longitudinal section of 



marginal portion of valves in connexion with the mantle, much magnified; 



