# 



Under surface of do. 

 (Mag. eight diameters.) 



30 FAMILY 



Fig. 6. 5, c), as to terminate in their centres 



in obtuse points. With these slia- 

 green-like scales, the heads, bodies, 

 and fins of all the species of at least 

 two of the Acanth genera, — Cheir- 

 acanthus and Diplacanthus, — were 

 as thickly covered as the heads, bo- 

 dies, and fins of the sharks are with 

 Section of shagreen of their shagreen; and so slight was 



Scy Ilium, Stellare. ,i -. r- • -u • x- xu x xi 



Under surface of do. *^« ^«g^«« ^^ imbrication, that the 



Section of scales of Cheir- portion of each scale overlaid by the 

 acanthus Microlepidotus. ^^^ g^^j^g ^^ immediate advance of 



it did not exceed the one-twelfth 

 part of its entire area. In the scale 

 of the Cheiracanthus we find the covered portion indicated 

 by a smooth, narrow band, that ran along its anterior edges, 

 and which the furrows that fretted the exposed surface did 

 not traverse. It may be added, that both genera had the 

 anterior edge of their fins armed with strong spines, — a cha- 

 racteristic of several of the placoid families. 



In the Dipterian genera Osteolepis and Diplopterus, the 

 scales were more unequivocally such than in the Acanths, 

 and more removed from shagreen. The under surface of 

 each was traversed longitudinally by a raised bar, which at- 

 tached it to the skin, and which in the transverse section 

 serves to remind one of the shagreen footstalk. They are, 

 besides, of a rhombodial form ; and, when seen in the finer 

 specimens, lying in their proper places on what had been once 

 the creature's body, they seem merely laid down side by side 

 in Ime, like those rows of glazed tiles that pave a cathedral 

 fioor ; but on more careful examination, we find that each 

 little tile was deeply grooved on its higher side and end (for 

 it lay diagonally in relation to the head), like the flags of a 

 Btone roof (fig. 6, a), — that its lateral and anterior neigh* 



