PLAGIOBRISSUS GRANDIS. 207 



Plagiobrissus. 



Pomel, 1883. Class. Meth. Ech., p. 29. 

 Type, Spatangus pectoralis Lamarck, 1816 = Echinus grandis Gmelin, 1788. Linn6, Syst. Nat., ed. 



13, 1, pt. 6, p. 3200. 



This group is rightfully distinguished from Metalia as it not only differs 

 markedly from that genus structurally, but its geographical distribution is wholly 

 different. Metalia is an Indo-Pacific genus while Plagiobrissus is confined to 

 certain parts of the tropical Atlantic and of the western Mediterranean. Louis 

 Agassiz first recognized the group but his name Plagionotus being preoccupied, Mr. 

 Agassiz, in the Revision, simply merged the component species with Metalia of 

 Gray, the most nearly allied genus, and there the matter has since rested, except 

 that Pomel, in his remarkable but generally ignored work, suggested the name 

 Plagiobrissus as a substitute for Plagionotus. It is regrettable that the species 

 of this genus are little known. The West Indian species seems to be fairly 

 common at the Bahamas, but the African species is no better known than when 

 first described fifty years ago, and the Mediterranean species is also very rare. 



The pedicellariae in this genus are notable and are abundant. The char- 

 acteristic form is a highly modified "long, globiferous," in which the valves 

 have become almost solid masses of calcareous matter. A normal form of 

 globiferous pedicellaria may also be present and rostrate pedicellariae are com- 

 mon. Tridentate pedicellariae with long valves having coarsely serrate or den- 

 tate margins occur and smaller tridentate and triphyllous are also present. 

 Ophicephalous pedicellariae may be present or wanting. 



Key to the Species of Plagiobrissus. 



Large primary tubercles present in dorsal parts of interambulacra 1, 2, 3 and 4. 



Peristome squarish, rarely more than twice as wide as long grandis. 



Peristome crescentic, more than twice as wide as long africani*s. 



Large primary tubercles on dorsal surface, confined to interambulacra 1 and 4 costae. 



Plagiobrissus grandis. 



Echinus grandis Gmelin, 1788. Syst. Nat., ed. 13, 1, pt. 6, p. 3200. 



Metalia pectoralis A. Agassiz, 1872. Rev. Ech., pt. 1, p. 144. Et auct. omnes post. 



Plagiobrissus pectoralis Pomel, 1883. Class. Meth. Ech., p 30. 



Plate 146, figs. 21, 22. 



It is hard to see why Mr. Agassiz chose to ignore Gmelin 's highly appro- 

 priate name in favor of Lamarck's name of twenty years later. No echinoid so 



