BRITISH FOSSILS. 



Decade YIII. Plate X. 



PTCNODUS LIASSICUS. 



[Genus PYCNODUS. Agassiz, (Sub-kingdom Yertebrata. Class Pisces. Order 

 Goaiolepidoti. Family Pyenodontidse.) Body short, deep, and adpressed ; three or five 

 rows of smooth, flattened, oblong, tritoral teeth, on each ramus of the lower jaw ; five 

 rows of similar teeth on the vomer ; incisive teeth in both jaws.] 



Pycnodus liassicus, Sp. Noy. 



Description. — The announcement of the occurrence of fishes 

 belonging to the family Pycnodontidce, in the lias of Great Britain 

 and Wurtemberg, recently made in a memoir read at the Geological 

 Society,* has been quickly followed up by the discovery of a true 

 Pycnodus, from the same formation. This interesting specimen was 

 brought to light during the operation of transferring the fine collec- 

 tion of fossil fishes in the British Museum, from the cases in Room 6, 

 to their new position in Room 2. It is supposed to have been 

 derived from the lias of Barrow-on-Soar, and, although far from 

 perfect, is, nevertheless, sufiiciently so to leave no doubt as to its 

 natural afiinities. In referring it to the genus Pycnodus, I have 

 been guided mainly by the characters of the dentary apparatus. 

 The general contour of the body has more resemblance to a Microdon, 

 or a Gyrodus, and wants the elongated caudal pedicle of the typical 

 Pycnodi ; but the characters of the teeth are so decisive, that I have 

 no hesitation in referring it to the latter genus. The specimen 

 figured in the plate measures from the symphisis of the lower jaw 

 to the commencement of the tail, 4 inches. The greatest depth, 

 following the direction of the dorso-ventral series of scales, is 3^ 

 inches. The anterior portion of the trunk is highly vaulted ; the 

 summit of the nape being nearly 1 inch higher than the occiput. 

 The frontal and facial line is straight, and steeply inclined. The 

 lower jaw is unusually large (fully 1 inch in length), and renders 



* Quarterly Journal of Geol. Soc, 1853, page 276. 

 [VIII. X.] 8 L 



