THE GEOLOGIST. 
JULY 1863. 
ON A NEW SPECIES OF HYBODUS EEOM THE LOWEE 
CHALK. 
Bt S. J. Mackie, F.G.S. 
Since the publication of Agassiz' * Poissons Fossiles ' only one addi- 
tion, that we arie aware of, has been made to our knowledge of this 
interesting genus of fishes, — certainly, at least, in respect to British 
geology. In 1845 Sir Philip Egerton described, before the Geological 
Society, a large jaw, or rather mouth of teeth, of a fish of this kii.d, 
found by Captain Ibbetson in the Isle of Wight, and named by Sir 
Philip Hyhodus hassanus. 
This species has been assigned to the Lower Greensand, in Morris's 
Catalogue, but the bed seems, from Sir Philip's statement, to be in a 
dubious position, for he speaks of it only as " near the junction of the 
Lower Greensand and Wealden," and says the specimen was sent to 
him " in the hopes it might tend to show to which of the two forma- 
tions its bed should be assigned," — a question he further declines to 
answer, as " the evidence it affords on this question is neither direct 
nor conclusive, inasmuch as it is an undescribed species ; and conse- 
quently any deductions beyond those based upon general affinities 
would be unwarrantable." Sir Philip adds, however, further on : 
" The geological inferences afforded by the specimen are briefly told. 
The species is new. The genus is undoubtedly Hybodns. This genus 
attains its maximum expansion in the Oolitic series, but it ranges 
from the Muschelkalk to the Chalk inclusive. The only evidence of its 
occurrence in the latter formation is a fragment of an ichthyodorulite 
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