LOWER MAGNESIAN LIMESTONE OF SUNDERLAND. 217 
the other includes the anterior and adjoining intermediate plate, 
and has apparently belonged to an individual larger than the 
first. 
4, Leda speluncaria, Geinitz. Deutsch. Zechst. p. 9, tab. 4, fig. 6. 
Casts of separate valves of this shell are pretty common. 
They vary in size; the largest are }{ths. of an inch in length. 
The hinge teeth are well shown; and the umbonal ridge is well 
marked, as if the individuals had been thick-shelled. 
5. Spirifera Urii, Fleming. Hist. ot Brit. Anim. p. 376. 
This shell is also comparatively common; but always occurs 
in detached valves. Some of the specimens are extremely 
minute ; others are larger than I have ever seen this species, 
being fully ,3,ths. of an inch in width. 
6. Camarophoria crumena, Martin. Petrif. Derb., p. pl. 386, 
fig. 4. 
T have only a single fragment of this shell, but as it shows 
part of the ventral valve, with the arched dental plates, it quite 
suffices to identify it. 
7. Chonetes, sp. 
With the preceeding species haye also occurred several speci- 
mens of an undoubted Chonetes. The largest specimens are 
+iths. of an inch in width, and 5°,ths. or rather more, in length. 
Some are semicircular in outline; others are more oblong; the 
dorsal line is slightly angulate in both forms. The valves are 
moderately convexo-concave; and they show traces of concentric 
lines of growth, but none of the radiate striation that usually 
characterises shells of this genus. Four or five cardinal spines 
are placed on each flank of the umbone. 
In 1856 Baron Von Schauroth described a Chonetes from the 
Mergelschiefer of Ilmenau, under the name of C. Davidsoni. The 
specimens from which he described appear to differ from mine in 
being less than half the size, of greater relative width, in having 
the surface ornamented with radiating strie crossed with con- 
centric lines of growth, and in possessing only three cardinal 
