Studies of Jamaica Echini. 147 



The upper ends of the auricles at this early stage are slightly flattened, but 

 do not arch over the ambulacrum at all. In a specimen 10 mm. in diameter, 

 the apophyses have developed somewhat, and the auricles are inclined over 

 the ambulacral area, but do not meet (fig. 4). In specimens 25 mm. in 

 diameter the apophyses have developed into distinct elevated ridges, and 

 the auricles have met over the ambulacral areas as slender arches (fig. 5). 

 From this point on to the adult the development of the perignathic girdle 

 is marked by the increase in height of the apophyses and concurrently the 

 increase in height and the lamellar expansion of the auricles (figs. 6, 7). 



In seeking comparisons to these stages of Centrechinus in the adults of 

 related forms, it is found in Aspidodiadema meijerei (Doderlein), A. nico- 

 haricum Doderlein, and Dermatodiadema horridum A. Agassiz, representing 

 the family Aspidodiadematidse, that the auricles exist as small conical spurs 

 situated on either side of the ambulacral areas, and apophyses are not 

 developed (fig. 2). This condition corresponds with the first stage noted 

 in the development of Centrechinus (fig. 3). This relation of the perignathic 

 girdle is of much interest because in the Aspidodiadematidse the simple 

 ambulacral plates, the large primordial ambulacral plates on the peristome, 

 the large apical disk and simple spur-like auricles are all primitive characters, 

 indicating that the family is more primitive structurally than is the still 

 primitive family of the Centrechinidse. While primitive in many char- 

 acters, the Aspidodiadematidse is specialized in that all the oculars reach 

 the periproct, and Centrechinus, while belonging to the primitive suborder 

 Aulodonta, is specialized in its great development of the perignathic girdle. 

 This shows how primitive and specialized features may be combined in one 

 and the same type. 



Mr. Agassiz (Panamic Echini, 1904, p. 59) says of the Aspidodiade- 

 matidse: "The auricles are most irregularly developed. They are either 

 wanting or mere projections, slightly raised." I have examined three rep- 

 resentative species and a number of specimens of this family, and find 

 no evidence that the auricles are irregularly developed. In adults they are 

 not wanting except where broken off. They are perfectly definite spur- 

 like projections, and of much interest as being structurally the most primi- 

 tive auricles known in any of the adult Centrechinoida. As the Cidaroida 

 have apophyses but no auricles, and as these structures make their first 

 known appearance in the Centrechinoida, the simplicity of their structure 

 in adults of the Aspidodiadematidse and in the young of Centrechinus is of 

 particular interest. 



ToxoPNEUSTES VARIEGATUS (Lamarck). 



A common species at Montego Bay is Toxopneiistes variegatus (Lamarck) , 

 which is found abundantly on the grass-covered bottom in shallow water. 

 Specimens attain a large size, some measuring 70 mm. in diameter. Few 

 young specimens were found, though this is perhaps due to the fact that 

 special search was not attempted, from limitations of time. The test is 



