472 Davis—On the Fossil Fishes of the Chalk of Mount Lebanon 
Family. SCYLLIIDZ. 
Genus. Thyellina. Munster. 
Thyellina; Miinster. L. Acasstz, 1836. ‘Rech. sur les Poissons Fossiles,” 
vol. i., p. 378. 
The type specimen of this genus was named by Count Miinster, but not 
described. It is from the cretaceous formation of Baumberge, near Miinster, 
and was sent to the late Professor L. Agassiz when he was preparing his great 
work on fossil fishes. The latter states that ‘‘Ce fossile a la forme ordinaire 
des vrais Scyllium, seulement la premitre dorsal est peu en arritre des ventrales, 
tandis que la seconde dorsale, qui est plus grande que l’anale est apposée & cette 
dernitre nageoire, comme dans le genre Ginglymostoma, mais un peu plus 
reculée. ‘Toutes ces nageoires ont leur angle antérieur arrondi; les pec- 
torales sont également trés-arrondies. La caudale est courte et son lobe antérieur 
faiblement échaneré. L’esptce type du genre est le Thyellina angusta, Miinst. 
(op. cit., Tab. xxxix., fig. 8). Sa forme est cylindracée et va en s’atténuant 
insensiblement jusquw’ & la base de Ja caudale, dont l’extrémité posterieure est 
arrondie. Ses verttbres sont un peu plus courtes que hautes et déprimées sur le 
milieu de leur longeur.” 
Professor Agassiz also described a second species from the Lias of Lyme Regis 
under the specific name Thyellina prisca. The specimen consisted of a series of 
vertebrz resembling those of T. angusta, Miinst., and was placed in the genus with 
considerable hesitation. Subsequent discoveries of better preserved specimens 
enabled the late Sir Philip Egerton (Memoirs of the Geological Survey, Decade 
XIII., pl. vu.,) to detect that the first and second dorsal fins carried spines similar 
to those of the Spinacide, and that consequently the fish could not belong to 
the genus Thyellina, which has no dorsal spines. He therefore instituted a new 
genus for its reception, Paleeospinax. 
The genus Palzoscyllium was formed for the reception of a fossil fish from 
the chalk formation of Arenfeldes, in Westphalia, by Dr. W. von der Marck, and 
is described in “‘ Palaeeontographica,” vol. xi. (1863-4), p. 66, plate vu, figs. 6-9. 
The ventral surface of the specimen is exposed; it is about 16°5 inches in length, 
and nearly 2 inches in height. The pectoral fins, a part of a ventral fin, and 
the second dorsal fin are exposed ; a long fin at the root of the tail is considered 
as the anal. The first dorsal fin is not visible, and its position relative to the 
ventral fins cannot therefore be ascertained. The posterior margin of the second 
dorsal overlaps, to some extent, the anterior portion of the anal. The vertebra, 
120 in number, are longer than high. The snout is broadly rounded, the mouth 
situated an inch behind its extremity. The teeth are similar in form to those 
