THE COMMON BRITISH STURGEON. 9 



many of which emit prickles. The Schypa is var. and y 

 of the Sturio of Pallas, who obtained it in the Wolga and 

 Obi. 



Age changes the form and size of the body-shields of 

 the Sturgeons, their crests becoming lower and blunter, 

 and their disks smaller, so that in aged fish the sharply- 

 pentagonal form of the body is lost, and the ventral 

 shields often wholly disappear. 



The fins, seven in number, are sustained by crowded 

 jointed, and generally flexible rays, finely serrated on 

 the edges ; the short graduated rays in front of the dor- 

 sal and anal are more or less bony. The anal is situated 

 under the posterior part of the dorsal, which is itself 

 placed far back. A stout, tall, bony first ray supports 

 the pectoral fin. 



The skull is cartilaginous throughout, but is supported 

 beneath by an osseous occipito-sphenoidal plate, which 

 extends posteriorly under five cervical vertebrae, and is 

 prolonged anteriorly into a slender vomerine and eth- 

 moidal process ; protection is afforded to the skull above 

 by a vaulted crust of ganoid scales or shields, which have 

 received names from Kittary,* Fitzinger and Heckel f 

 and others, accordant with the regions that they cover. J 

 In the views of the upper surface of the head introduced 

 in the subsequent pages, the posterior mesial shield is the 

 first of the dorsal series ; anterior to it is the single 

 occipital shield also occupying a mesial place ; and whose 

 anterior process enters some way between the coronal or 

 parietal shields which form a pair and come in contact 



* Dr. Modeste Kittary : Bull, de la Soc. Imp. des Natur. de Moscov. 

 1850. 



-j- Annalen der Wien. Erster Band. 



J Professor Owen observes that the attempt to ascertain the homologies of 

 these cranial shields with the true epicranial bones of osseous fishes is diffi- 

 cult and unsatisfactory. 



