154 T. Davidson — What is a Brachiopod ? 
26. Dacidsonia Yerneuilii (fossil). To show the great thickness of tlie ventral valve 
a, and its mode of attackment to submarine objeets by a portion of tbe 
substance of tbis valve. b. dorsal valve ; d. small free space left for the 
animal. 
27 . Product us Llangollensis (fossil) . Longitudinal section to show tbe great differenee 
in thickness of tbe valves. a. ventral ; b. dorsal ; d. space left for animal. 
28. Strophomena filosa (fossil). To sbow tbe small space left for tbe animal between 
the valves. 
29. TFaldheimia Jlavescens. Enlarged section of shell (after King), o. tkick cal- 
careous innermost division ; n. intermediate thin calcareous division ; m. outer 
division of tbin membrane ; e. f. canals traversing tbe calcareous layers 
o and n ; the lower half of the Perforation being considerably smaller in 
diameter than the upper one. 
30. Terebratula bullata (fossil). Section of shell near the external surface and 
parallel to it, sbowing tbe remarkably large size and close proximity of tbe 
perforations. 100 diameters. 
31. TFaldheimia flavescens or australis. Internal surface of the shell, showing tbe 
imbricated arrangement of tbe extremities of tbe prisms, which are seen 
longitudinally at b, magnified 100 diameters. 
32. Vertical section, considerably enlarged, so as to show the ordinary 
trumpet-like form of the vertical passages and remarkable condition which 
they exbibit in tbe inner and (probably) later-formed layer. 
33. Rhynchonella psittacea. Portion of the internal surface of tbe shell more kighly 
magnified, sbowing tbe imbricated arrangement and tbe entire absence of 
perforations, magnified 100 diameters. 
34. Portion of tbe shell, showing at a the internal surface, with the 
imbricated arrangement of tbe extremities of its component prisms, and at 
b tbe aspect of tbe prismatic substance as displayed by a fracture nearly in 
tbe direction of tbe length of tbe prisms, sbowing also entire absence of 
tbe least trace of perforations. Magnified 40 diameters. Figs. 30 to 34 
after Dr. Carpenter. 
35. Lingula anatina. Longitudinal section of tbe shell to show the alternation of 
calcareous and honiy layers ; b. b. calcareous layers perforated by minute 
canals ; d. d. borny layers. After Dr. Gratiolet. 
36. Grania anomala (enlarged). Inferior of tbe dorsal valve to sbow tbe position of 
tbe spiral appendages. From a specimen in tbe Museum of tbe School 
of Mines. 
fig. CLISTENTEEATA. PLATE VIII. 
1. Terebratula carnea (fossil). Inferior of tbe dorsal valve, to sbow tbe short 
simple loop. 
2. Terebratulina caput-serpentis. Interior of tbe dorsal valve, to show the ring- 
sbaped loop. 
3. Magas pumilus (fossil). Longitudinal section to sbow tbe large central septum 
and disunited deflected portion of the loop. 
4. Bouchardia tulipa. Interior of tbe dorsal valve, to sbow tbe anebor-sbaped 
apopbysis. 
6. Thecidium mediterraneum. Seen in profile. Tbe valves opened as in life. After 
Lacaze-Duthiers. 
6. Spirifer Schrenkii (fossil). Interior of tbe dorsal valve, sbowing the Cardinal 
process, quadruple impression of the adductor muscle, and one of the cal- 
careous spiral lamina; for tbe support of the labial appendages. 
7. Atrypa reticularis (fossil). Interior of tbe dorsal valve, sbowing tbe position 
and sliape of tbe spiral lamina; for tbe support of tbe labial appendages. 
8. One of the spiculae of the mantle of Terebratulina caput-serpentis highly mag. 
9. Rhynchonella psittacea (after Hancock) much enlarged. Dorsal view of the 
animal ; a. pallial lobe ; c. peduncle : d. great pallial sinuses giving off 
branches at the margin; i. extremities of adductor muscle; n. liver; 
x. spiral brachial apparatus ; z. genitalia and muscular ties uniting tbe 
walls of tbe genital sinuses. 
10. TFaldheimia australis (after Hancock). Diagram of longitudinal section of 
marginal portion of valves in connexion with tbe mantle, mueb magnified; 
