424 Mr. J. W. Davis on the Genera 
the ‘collapsed tentacles” of Pentremites obliquatus and of 
P. crenulatus respectively should have assumed shapes zn 
limestone which are so very different, but yet constant for those 
particular species. 
Dr. Hambach is understood to be at work upon a mono- 
graph of all the known American and European species of 
the Blastoidea. Its appearance will be awaited with no ordi- 
nary interest, in the hope of finding therein some further 
development of the remarkable new theories of the morpho- 
logy of the group which have been criticised above. 
XLIL— On the Genera Ctenoptychius, Agassiz; Ctenopetalus, 
Agassiz; and Harpacodus, Agassiz. By JAmEs W. Davis, 
HGS.) ELS: 
Pror. L. AGAsstz, in his great work on Fossil Fishes, defined 
the genus Ctenoptychius (Poiss. Foss. vol. 11. p. 99) as em- 
bracing small teeth presenting the appearance which would 
be produced if small teeth of Orodus were strongly compressed 
so that the transverse ridges of that genus were disposed in 
the form of comb-like projections more or less round and de- 
tached. The teeth of Ctenoptychius ave remarkable for their 
pectinated appearance and compressed form. 
Three species of this genus are described by Prof. Agassiz, 
viz. :—1, Ctenoptychius apicalis (p. 99, pl. xix. figs. 1, 1a) from 
the Staffordshire coal-fields and the coal strata near Man- 
chester; 2, C. pectinatus (p. 100, pl. xix. figs. 2, 3, and 4) 
from Burdie House and Lancashire; and 3, C. denticulatus 
(p. 101, pl. xix. figs. 5, 6, 7). ‘To those described were also 
added (p. 173) others which were named but not described, 
the description being left for a supplement, which unfortu- 
nately has not been written. They are :— 
Ctenoptychius cuspidatus. Coal, Glasgow. 
C. dentatus. Mountain Limestone, Armagh. 
CU. serratus. am - 
C. macrodus. Me i 
C. crenatus. Coal, Carluke, near Glasgow. 
In 1843 C. macrodus was described and figured in Port- 
lock’s Report on the Geology of Fermanagh &c. (p. 467, 
pl. xiv. fig. 7). 1t differs from C. apicalis, Ag., “by the form 
of the crest, which is round, and not tending to a point as in 
that species.” ‘The crest is denticulated, the denticles being 
tolerably large and blunt. 
Prof. M‘Coy, 1854 (Brit. Palesoz. Foss. p. 626), defined the 
