468 Davis—On the Fossil Fishes of the Chalk of Mount Lebanon, 
The fish remains from the cretaceous formation of Mount Lebanon are 
comprised in the two first classes. The sharks and rays are represented by 
several species in each group, and the Teleosteans are numerous and varied. 
There is a marked absence of Ganoids. The large number of fishes of the 
latter order, which formed so important a part of the Fauna of the Oolite and 
Liassic formations, have disappeared, and it is doubtful whether a single example 
has been found in the chalk of the Lebanon district. In accordance with the 
general character of the evidence afforded by the chalk strata, there is a decided 
advance towards the present existing Fauna. Some of the sharks have certainly 
a generic relationship with those now living, and the same observation may 
be applied to the rays. The Holocephala (Chimeroids) are not represented. 
The Teleosteans are for the most part, if not entirely, comprehended in the 
orders Acanthopterygii and Physostomi, and, as will be found hereafter, embrace 
many very peculiar forms. These groups appear to have taken the place of 
the Ganoids of the older formations, and although no direct proof of any process 
of evolution has hitherto been traced, there is strong presumptive evidence that 
some such process may have been in operation. 
Sub-class I—PALASICHTHYES. 
Heart, with a contractile conus arteriosus; intestine with a spiral valve ; 
optic nerves non-decussating, or only partially decussating ; skeleton carti- 
laginous or osseous. 
This sub-class is divided into two orders: the Chondropterygii, and the 
Ganoidei: of the latter, as already observed, there are no representatives in 
the chalk of Lebanon. The former, comprising the sharks, rays, and chimeras, 
is thus defined by Dr. Giinther :— 
Order 1.—CHONDROPTERYGH. 
‘“‘ Skeleton cartilaginous. Body with medial and paired fins, the hinder 
pair abdominal. Vertebral column generally heterocercal; the upper lobe of 
the caudal fin produced. Gills attached to the skin by the outer margin, with 
several intervening gill-openings: rarely one external gill-opening only. No 
gill-cover. No air-bladder. Two, three, or more series of valves in the conus 
arteriosus. Ova large and few in number; impregnated, and in some species 
developed within the uterine cavity. Embryo with deciduous external gills. 
Males with intromittent organs attached to the ventral fins.” 
This order is divided into two sub-orders: the Plagiostomata and the 
Holocephala, the latter containing the chimeroid fishes, 
