from the Upper Silurian ‘Wenlock Limestone’ of Dudley. 97 
thin. Their external surface is ornamented by a very great num- 
ber of fine parallel striz or lines of growth; on the lateral and 
anterior sides of each plate, and between them, there are ex- 
tremely thin ribs covered with small granulations. Each of 
these plates appears to have undergone a suspension of develop- 
ment at about the middle of its growth; this interruption is indi- 
cated byastriation much larger and deeper than the others, which 
are all nearly equal in strength. The median and lateral areas are 
very nearly equal, and divide each side of the plate into two parts. 
t is probable that, if this species was furnished with 
apophyses, they were very small, as I have not been able to 
discover any trace of them on the various specimens I had the 
opportunity of examining. 
Relations and Differences.—This Chiton presents a greater 
similarity with C. priscus, Munster, and C. Mempiscus, De Ryckh. 
It differs from both, however, by the lateral margin of its plates 
being more even, by the slight thickness of its test, by the ab- 
sence of apophyses, and especially by the fineness and great 
number of strize covering its surface. 
Dimensions.—Length of the dorsal plate about 12 milli- 
metres; breadth of each side 10 mm., which gives for the com- 
plete animal an approximate length of from 80 to 90 millimetres, 
and a mean breadth of 16 to 18 mm. 
Locality.—This species has been discovered by Messrs. Gray 
and Fletcher in the Upper Silurian ‘ Wenlock limestone,’ near 
Dudley. 
2. Chiton Wrightianus, De Koninck. (PI. II. fig. 2a, b,c.) 
The form of the dorsal plates of this species is subtriangular, 
the posterior edges making very nearly a right angle. The 
lateral angles are rounded, and the anterior edge is very sinuous. 
All the plates are supplied with a well-marked median carina, 
and appear to have been without apophyses. The surface is 
covered with a small number of deep equidistant strie. The test — 
is slender. The median area is larger than the lateral one. 
Relations and Differences.—This Chiton very much resembles 
C. Loftusianus, King, but differs from it in the regularity of the 
striz of the median and lateral areas, and by the more marked 
sinuosity of the anterior edge of its plates. 
Dimensions.—The length of each dorsal plate is about 8 milli- 
metres, and the breadth 12 mm. 
Locality.—This species was found by Mr. Gray with the pre- 
ceding one ; it is, however, scarcer than even that. 
EXPLANATION OF PLATE II. 
Fig. 1a, Chiton Grayanus, De Kon., nat. size, with fragments of four 
Ann. & Mag. N. Hist. Ser. 3. Vol. vi. 7 
