Davis—On the Fossil Fishes of the Chalk of Mount Lebanon. 469 
Sub-order 1.—PLAGIOSTOMATA. 
“From five to seven gill-openings. Skull with a suspensorium and the 
palatal apparatus detached ; teeth numerous.” 
The Plagiostomata may be divided into two groups—the (A) Selachoidei, or 
sharks, whose body is elongate, more or less cylindrical, gradually passing into the 
tail; gill-openings lateral. 
The (B) Batoidei, or rays, in which the body is depressed, and surrounded by 
immensely developed pectoral fins, forming a broad flat disc. Caudal portion more 
or less rapidly contracted to form the tail. Gill-openings, five in number, are 
always placed on the abdominal surface of the fish. 
The sharks are all of a small size, rarely, if ever, exceeding two feet in length: 
in this respect they differ very materially from the great Selachians of the earlier 
formations: they exhibit still greater divergence in the state of their preservation ; 
for whilst the earlier fishes are represented in the fossil state, only in the most 
fragmentary form, those of the Lebanon are beautifully preserved, and exhibit 
considerable details of structure. The state of their preservation, considering the 
cartilaginous nature of the skeleton, apparently points to the extremely quiet and 
unruffled period during which the chalk was deposited. Had the fish been sub- 
jected to the action of the tides only, they must have been dismembered by the 
decomposition of the connecting cartilages; and had such been the case, there 
would have remained only a mass of indeterminate fragments, consisting of 
vertebree and teeth, with occasionally a small spine. The special characteristics of 
the several members of this group will be enumerated in the detailed descriptions 
further on: at present it will be sufficient to observe that Notidanus gracilis is some- 
what nearly related to some species of the same genus from the chalk of Sussex. 
Spinax primzevus appears to be an intermediate form between the Spinax of the 
Lias and the Dog-fishes now existing, and Scyllium Sahel Almz, a diminutive 
form, bearing a close resemblance to the smooth hound, also common in the waters 
on our own coast. 
The number of genera and species of the Selachoidei has been largely 
increased during the past few years by the careful efforts of the Rev. E. R. 
Lewis, for some time at the Protestant Syrian College at Beyrout, who neglected 
no opportunity to collect every new example brought to light. The same observa- 
tion applies with equal force to the second group of the Plagiostomata; and 
the knowledge of the fossil rays of the Lebanon chalk has been greatly 
extended by his well-directed energy. The sharks, with the exception of the 
genus Spinax, have been obtained from the soft chalk of Sahel Alma: Spinax 
is found both in that locality and at Hakel. The rays are more equally divided 
between the two localities; five species have been discovered in the hard 
TRANS, ROY. DUB. SOC,, N.S. VOL, III, 3T 
