80 
ICHTHYOLOGY 
MONACANTHUS MARGARITIFER. 
Monacanthua Perulifer, Cast. Olim. 
This sort, which appears to me not to have yet been de- 
scribed, belongs to the division with : " Anal fin with less than 
forty rays ; dorsal spine with four series of barbs j the front 
series much closer together than the hinder series, and formed 
by small barbs." 
This species would probably enter in Dr. Blecker's genus 
Pseudomonacanthus. 
The upper profile of the head is rather concave ; the gill 
opening is situated below the two posterior thirds of the 
orbit ; the distance from the extremity of the snout to the 
gill-opening is contained three and two-third times in total 
length of the fish, including (as always) the caudal ; diameter 
of the eye three times in the same ; the lower profile forming 
an extended triangular pouch ended by the ventral star ; the 
distance from the end of this ventral spine to the back is not 
included quite once and a half in the total length. 
The whole body is covered with papillae, each terminated like 
a small mushroom or a pearl. 
The first dorsal is formed of one large spine and of one short 
ray ; the spine is rather arched and about as long as the dis- 
tance from the anterior extremity of the snout to the centre 
of the orbit ; it has four ridges, the two front ones placed 
very near one another and only separated by a longitudinal 
sulcate ; they are armed with a series of small spines directed 
downwards; those of the posterior ridges are much 
larger, arched, and also directed downwards ; the 
second dorsal is rather high, and formed of twenty- 
seven rays; the caudal is as long as the distance from 
the snout to the first third of the orbit ; it is rounded and 
formed of nine rays ; the anal is similar to the second dorsal, 
and composed of the same number of rays ; the pectorals are 
rather short; their length being contained twice in the distance 
from the snout to the centre of the orbit ; they are formed of 
twelve rays. 
The ventral star or spine is anchylosed to the pelvic bone ; 
