SECTION III. 
Either no ligament, or none known ; or represented by a tendinous cord, which supports the shell. 
This Section contains Two Families Rudista, and Brachiopoda. 
RUDISTA 6 Genera. 
Ligament, hinge, and animal unknown; shell very inequivalve. No distinct beaks. 
Spieerulites. — Shell inequivalve, orbicular-globose, rather depressed above, echinated 
externally with large, subangular, horizontal scales ; upper valve smallest, rather 
flat, opercular ; the internal surface furnished with two unequal, subconical, curv- 
ed, and prominent tuberosities; lower valve largest, rather ventricose, the exter- 
nal margin radiated with scales ; cavity obliquely conical, and forming on one side, 
by the folding of the internal margin, a crest, or projecting keel: internal side of 
the cavity transversely striated. Hinge unknown. 
Plate XXI. Fig. 6. S. foliacea. Fossil. [Icon. — Encyc. Method, pi. 172. fig. 7-] 
IIadiolites. — Shell inequivalve, externally striated; the strite longitudinal, radiating: 
lower valve turbinated, and largest ; the upper, convex or depressed conical, oper- 
cular. Hinge unknown. 
Plate XXI. Fig. 7» It. turbinata. [British Museum.] 
Calceola. — Shell inequivalve, triangular, turbinated, flattened beneath ; the larger valve 
hollowed or liood-shaped, obliquely truncated at the aperture; the cardinal mar- 
gin straight, transverse, a small notch or indentation in the middle ; the superior 
margin arched : the small valve flat, semi-orbicular, opercular, having a tubercle 
on each side of the cardinal margin, and, in the middle, a pit with a small lamina. 
Plate XXI. Fig. 8. C. sandalina. [Mr. J. D. C. Sowerby’s Cabinet.] 
Birostrites. — Shell inequivalve, bicornute, the disk of the valves elevated conically, un- 
equal, obliquely diverging, nearly straight, horn-shaped, the one enveloping the 
other at the base. 
Plate XXI. Fig. 9. B. insequiloba. [Mr. J. D. C. Sowerby’s Cabinet.] 
Discina. — Shell inequivalve, oval-rotundate, rather depressed, valves nearly equal, each 
having an orbicular disk in the centre, very distinct ; disk in the upper valve not 
perforated, with a mammillated protuberance in the middle; that in the other valve 
very white, divided by a small transverse slit. 
Plate XIII. Fig. 2. D. Norvegica. (Orbicula Norvegica. — Sowerby’s Genera.) [Mr. G. B. Sower- 
(«) Lower valve of ditto. by’s Cabinet.] 
(b) Upper valve of ditto. 
Crania. — Shell inequivalve, suborbicular, lower valve almost flat, perforated in the in- 
ternal surface by three unequal and oblique holes ; the upper valve very convex, 
furnished interiorly with two prominent callosities. 
Plate XIII. Fig. 3. C. personata. (Anomia craniolaris.— Linn.) 
(a) Lower valve of ditto. 
( b ) Upper valve of ditto. 
