FROM THE YOREDALE SERIES. 623 
dale are the highest beds in which it has been recorded. In the 
more recent members of the Carboniferous series it appears ta be 
quite extinct. 
Genus Pristopus, Agass. MSS.; Davis, Trans. Roy. Dubl. Soc. 
n. 8. vol. 1. p. 519 (1882). 
Pristopus Fatcatus, Ag.; Davis, l. c. p. 519, pl. lxi. figs. 17-22. 
(Plate XXVI. figs. 19, 20.) 
Genus Copopus, Agass. MSS.; Davis, Trans. Roy. Dubl. Soc. 
n.s. vol, i. p. 464 (1882). 
Coropus cornutus, Agass.; Davis, Ul. c. p. 464, pl. lviu. figs. 1-5. 
(Plate XX VII. fig. 22.) 
Psammodus cornutus, Agass. Poiss. Foss. vol. iii. p. 174 (1838). 
Teeth. Subquadrate, anterior margin more or less circular, lateral 
ones nearly straight and diverging posteriorly. Posterior margin 
concave. Postero-lateral angles produced beyond the tooth and 
forming horn-like processes. Crown slightly convex where unworn, 
but central portion deeply concave, and considerably worn by 
attrition towards the anterior extremity. A slight depression 
extends inside each lateral margin, which is slightly elevated. 
Surface enamelled, closely covered with minute punctures. Base: 
surface roughly striated longitudinally, slightly concave, thickest 
in the centre and thinning off towards each side; posteriorly, it 
extends beyond the surface of the crown, apparently to afford sup- 
port to the anterior portion of a succeeding tooth. 
This species is extremely rare in the limestones at Leyburn. 
Genus Crenoprratus, Agass. MSS.; Davis, Trans. Roy. Dubl. Soc. 
n.s. vol. i. p. 511 (1882). 
CrENOPETALUS CRENATUS, Davis, J. c. p. 513, pl. lxi. fig. 9. (Plate 
XXVII. fig. 18.) 
This species is readily distinguished from C. serratus, Ag., from 
the Armagh limestone, by its more graceful form and generally 
more fragile appearance. The serrations or small denticles forming 
the apex of the crown are smooth and rounded, whilst those of 
Otenopetalus serratus are subdivided into still smaller serrations. 
The plications or folds of ganoine forming the anterior base of the 
crown are in greater number, and they form an acute angle, 
pointing towards the base in the species now described, whilst in 
C. serratus the base of the crown is more or less curved. 
Genus Dictrropvus, Davis, Trans. Roy. Dubl. Soe. n. s. 
vol. i. p. 410 (1882). 
Dictiropus scrruLus, Davis, J. c. vol. i. p. 410, pl. li. fig. 29 
(1882). (Plate X XVII. fig. 12.) 
This species resembles Orvodus to some extent in structure, but its 
a 
