ITS STRUCTURE, BULK, AND ASPECT. 67 



shape, but not rarely confluent, or of an elongated or bent 

 form j and when to these the characteristic rays were added, 

 the stars produced were of a rather eccentric order, — stars 

 somewhat resembling the shadows of stars seen in water. In- 

 dividual specimens have already been found, on which, if we 

 recognise the form of the tubercle as a specific character, se - 

 veral species might be erected. The 

 accompanying woodcut (fig. 25) re- 

 presents, from a Thurso specimen, 

 what seems to be the true normal 

 pattern of these cerebral carvings. 

 Seen in profile (6), the tubercles re- 

 semble little hillocks, perforated at 

 their bases by single lines of thickly- 

 set caves : while seen from above (a\ dermal tubercles of Astero- 

 - . - , 11., lepis. 



the narrow piers of bone by which /t.^ ^ •,. ^ x 

 ■^ , , "^ (Mag. two diameters.) 



the caves are divided take the form 



of rays. The palaeontologist will scarce fail to recognise in this 

 print the coral Monticularia of Lamarck, or to detect, in at 

 least the profile, the peculiarity which suggested the name. 



The scales which covered the creature's body (fig. 26) were, 

 in proportion to its size, considerably smaller and thinner than 

 those of the Holoptychius, which, however, they greatly re- 

 semble in their general style of sculpture. Each, on the lower 

 part of its exposed field, was, we see, fretted by longitudinal 

 anastomosing ridges, which, in the upper part, break into de- 

 tached angular tubercles, placed with the apex downwards, and 

 hollowed, leaf-like, in the centre ; while that covered portion 

 which was overlaid by the scales immediately above we find 

 thickly pitted by microscopic hollows, that give to this part 

 of the field, viewed under a tolerably high, magnifying power, 

 a honeycombed appearance. The central and lower parts of 

 the interior surface of the scale (a) are in most of the speci- 

 mens irregularly roughened ; while a broad, smooth band. 



