194 
SEIACHir. 
P. 1446. Four imperfect specimens ; Armagh. Egerton Coll. 
46042. Large abraded specimen ; Beith, Ayrshire. 
Presented by Robert Craig , Esq ., 1874. 
P. 5354. Five fragments of abraded dental plates detached from 
the matrix, one being shown in PI. I. fig. 22; Ticknall, 
near Melbourne, 8. Derbyshire. Wilson Coll. 
(ii.) u Lower ” dental 'plates. 
P. 2471-4. Four specimens figured by J. W. Davis, loc. cit., under 
the name of X. striatus ; Armagh. Enniskillen Coll. 
P. 2475 a. Six similar specimens ; Armagh. Enniskillen Coll. 
P. 1446 a. One dental plate ; Armagh. Egerton Coll. 
Xysti?©dng verus, St. John & Worthen. 
188-3. Xystrodus vents , St. John & Wortlieu, Pal. Illinois, vol. vii. 
p. 181, j)! viii. figs. 6, 7. 
Type. Detached dental plates. 
Transverse stria? upon the coronal surface large, irregular and 
wavy, coalescing and bifurcating. “ Upper ” dental plates regularly 
triangular, the inner margin of the adult having an average measure¬ 
ment of about 0-009, the distance from the outer apex to the inner 
margin being about 0*02; anterior coronal elevation prominent and 
the antero-lateral border abruptly descending almost vertically from 
its summit. 
Form. Sf Loc. Chester Limestone (Lower Carboniferous): Illinois, 
U.S.A. 
P. 2479. Two u upper ” dental plates detached from matrix ; horizon 
unrecorded, but probably from the Chester Limestone. 
Enniskillen Coll. 
Xystrodus (?) egertoni 5 Davis. 
1883. Xystro.dus egertoni, J. W. Davis, Trans. Roy. Dublin Soc. [2] 
vol. i. p. 450, pi. lv. figs. 22, 23. 
Type. Abraded dental plates ; British Museum. 
Founded upon comparatively massive, abraded dental plates, with 
an irregular coronal surface, exhibiting little concavity, and large 
punctations only indistinctly arranged in transverse rows. More 
