462 DR JOHN ALEXANDER SMITH ON CALAMOICHTHYS, 



occipital plate is smaller in size, and somewhat triangular in shape, the straight base 

 being in front, and the lateral margins terminating in a pointed posterior extremity. 

 Between these supra occipital plates, laterally, and the smaller ossicles, to be 

 afterwards noticed, which run along the sides of the head, there are other two 

 small bony plates, on each side of the nape. One in front, the smaller, triangular 

 in form, is the epiotic plate of Professor Huxley ; it lies to the outside of the 

 external supra occipital plate, and behind it lies the second, the supra scapular 

 plate, somewhat larger, and more rhomboidal in shape, its longest diameter 

 being outwards and backwards, it fills up the angular space behind the internal 

 supra occipital plate, and the series of lateral ossicles ; completing thus the 

 covering of the upper and back part of the cranium. (Plate XXXI. fig. 6.) 



In the mesial line, immediately behind and between the two internal supra 

 occipital plates, lies the first of the true scales of the body on the dorsal surface, 

 from which a row of scales passes the posterior margin of the supra scapular 

 plate, and runs diagonally backwards and downwards along each side of the body. 



The bony plates which cover the lateral and back parts of the head, consist, 

 first, of a series of small ossicles, which commence a little behind the orbits, and 

 run in a curved direction upwards and backwards, along the external margins of 

 the frontal and other cranial plates, which have just been described, to the back 

 part of the head. These small plates vary in shape from somewhat quadrate to 

 triangular forms, and they also vary in number on the different sides of the head, 

 being in this specimen ten on the one side and eleven on the other. Two of these 

 small bones — which lie alongside the parietal bones, and behind the extremities of 

 the transverse suture between them and the frontal bones, on each side of the head 

 — have their inner margins free or unattached to the adjoining bones. This enables 

 them to be raised up and opened, like a valve, which communicates with the 

 branchial cavity. They have accordingly been styled the spiracular ossicles, which 

 may be a sufficient designation for the whole series— those in front, between them, 

 and the orbit, numbering some four or five bones, have, however, been named the 

 supra temporal ossicles ; and the plates placed behind these spiracular ossicles, are 

 three or four in number, they continue the series along the upper margin of the 

 operculum, and may therefore be styled the supra opercular ossicles. Outside and 

 immediately below the supra temporal and spiracular ossicles the front of 

 this series of small bones, and at a little distance behind the orbit, there is a 

 larger, somewhat oval-shaped plate, the preoperculum of Agassiz, which runs 

 backwards nearly to the line of the posterior margin of the parietal bones ; and 

 immediately behind it lies the still larger and broader operculum, an irregularly 

 four- sided plate of bone, its anterior and superior margins being nearly straight, 

 its posterior by far the shortest, and its lower and external margin much 

 rounded in its outline. Below these plates the sides of the head are simply 

 covered with soft and smooth skin, which expands into a free margin behind 



