FROM THE YOREDALE SERIES, 619 
portion of spine circular in transverse section; nearer the base 
the walls are thin, and the section is laterally compressed. The 
surface is uniformly but minutely striated. 
Genus Crapopus, Agass. 
Cladodus, Agassiz, Rech. sur les Poiss. Foss. vol. iii. p. 196 
(1833); McCoy, Brit. Paleeoz. Foss. p. 619 (1855). 
CLapopus mucronatus, Davis, Trans. Roy. Dubl. Soc. n.s. vol. 1. 
p. 380, pl. xlix. fig. 21 (1882). (Plate XXVIL. fig. 10.) 
Numerous teeth of this species, for the most part considerably 
smaller than the specimen described as above, occur in the limestone 
near Leyburn. As may naturally be expected, they offer con- 
siderable diversity of form. A specimen 0°5 inch in breadth across 
the base has a median cone wider at the base and shorter; it is 
somewhat widely expanded midway towards the apex as compared 
with the type. The lateral extensions of the base are deeply 
channelled vertically and highly polished on the surface. The base 
is considerably more rectangular than in the type. The cones are 
quite smooth. The divergence of this specimen is marked and it may 
possibly have belonged to another species ; but for the present, and 
until more distinctly confirmatory evidence shall be obtained, it 
appears advisable to place it with Cladodus mucronatus. 
In a third specimen, of about the same breadth as the last, the 
median cone is longer than usual, itis smooth with a deep and wide 
sulcus at the base, extending upwards more than half the length 
of the cone ; antero-posteriorly the cone is somewhat depressed, and 
the surface at each side thins out, so as to form a pointed keel. 
The keel descends to the basal portion, and is continued along the 
base and joins a similar projection from the sides of the secondary 
cones. Of the latter there are two on each side; they are large, 
acuminate, and partake generally of the character of the central 
one. 
Crapopus Hornet, Davis, Trans. Roy. Dubl. Soc. n. s. vol. i. p. 380, 
pl. xlix. fig. 20 (1882). (Plate XXVII. fig. 11.) 
Cladodus Hornet is readily distinguished from its nearest ally, 
Cladodus elongatus, Davis, by the absence of secondary cones. (C. 
elongatus, whichis found on the Mountain Limestone at Settle, many 
hundreds of feet lower in the series, is larger, and between the 
central cone and the two extreme lateral ones is possessed of several 
small intermediate denticles. The same difference also serves to 
distinguish this species from C. striatus, Agass., and in addition its 
central and lateral cones are proportionately very much longer and 
more attenuated. 
CLADODUS sTRIATUS, Agassiz. 
This species appears to be somewhat doubtfully represented in 
the limestone of Wensleydale. It occurs in considerable abundance in 
