86 



Tectospondyli. 



Table-case, 

 No. 31. 



Wall-case, 

 No. 3. 



Table-case, 

 No. 32. 



destitute of an anal fin, and their vertebrae, when fully devel- 

 oped, are strengthened by concentric layers of calcified tissue ; 

 they are hence named TECTOSPONDYLI (covered- vertebras) . The 

 " Sharks and Dog-Fishes " always exhibit an anal fin, and when 

 the vertebrae are strengthened, radiating plates predominate over 

 concentric plates; they are thus known as ASTEROSPONDYLI 

 (star-vertebrae). It is impossible as yet to make any satisfac- 

 tory arrangement of the ancestors of these two sub-orders 

 which are destitute of vertebrae, or have them only^ incom- 

 pletely formed. 



SUB-ORDER I. Tectospondyli. 



The Spinacidae, or spiny dog-fishes, of the present day are 

 supposed to be little-modified descendants of the early ancestors 

 of the rays ; but they are scarcely known among fossils. Well- 

 preserved fishes which seem to belong to the existing genera 

 Avanthias and Centrophorus, are exhibited from the Upper Chalk 

 of Mount Lebanon. The Petalodontidae, of Carboniferous and 

 Permian age, may perhaps be related to the Spinacidse, but they 

 are only known by fragments, chiefly teeth. Petalodus and 

 Polyrhizodus are Lower Carboniferous, while Janassa is both 

 Carboniferous and Permian. The existing Squatinidae date 

 back to the Lower Kimmeridgian, fine examples of Squatina 

 being known from the Lithographic Stone of Bavaria (Figs. 114, 

 115) . Detached teeth are exhibited from the English Cretaceous, 

 Eocene, and Pliocene Formations. The Pristiophoridae are 

 insignificant as fossils, and the Pristidae are represented 

 only by the Cretaceous Sclerorhynchus and by fragments of 

 Pristis-like " saws " from the Eocene and later deposits. 

 Sclerorhynchus atavus is a remarkable fish from the Upper 

 Chalk of Mount Lebanon, with the " saw " scarcely more 

 developed than that of a Pristiophorus. Numerous Rhino- 

 batidae, apparently identical with the existing Rhinobatus, occur 

 well-preserved in the Lithographic Stone of Bavaria and 

 France, and in the Upper Cretaceous of Mount Lebanon. The 

 fine slab of Rhinobatus (Spathokatis) bugesiacus affixed to 

 the wall between Wall-cases Nos. 2 and 3, is particularly 

 worthy of examination. The Bajidae and Trygonidae are 

 also represented by numerous fine specimens from the Upper 

 Chalk of Mount Lebanon, there being apparently Raja itself 

 and a small extinct sting-ray named Cyclobatis. Torpedos 

 occur in the Upper Eocene of Monte Bolca, near Verona, but 

 are not represented in the Collection. 



The Carboniferous teeth named Psammodus and Copodus may 

 belong to a family of devil-fishes, related to the modern 

 Myliobatidae, but their relationships are very uncertain. They 

 are always found detached, and a large series is exhibited from 



