Studies of Jamaica Echini. 157 



the dental capsules are large, embracing the base of the tooth as in the 

 Echinidse and Strongylocentrotidae. The perignathic girdle of Echino- 

 metra hicunter in the adult is highly specialized, having relatively high ridge- 

 like apophyses and extravagantly developed auricles which meet over the 

 ambulacra and are produced dorsally as spoon-shaped plates with a long 

 median symphysis (fig. 21). In young specimens, 5 mm. in length, the 

 auricles exist as simple erect styles situated on either side of the ambulacra 

 but not arched over the same (fig. 18). In specimens 10 mm. in length, 

 the auricles arch over the ambulacra, but are still separate, not meeting in 

 median suture (fig. 19). In a specimen 15 mm. in length, the auricles have 

 met over the ambulacra and are joined by median suture, and the apophyses 

 exist as moderately developed ridges (fig. 20). From here on to the adult 

 condition the apophyses increase in height and the auricles gradually take 

 on an extensive vertical enlargement of their upper border (fig. 21). In 

 Echinometra viridis A. Agassiz, E. ohlonga Blainville, and E. vanhrunti A. 

 Agassiz, in adults, the auricles are relatively slender, but are united in 

 suture over the ambulacra; there is no vertical extension in a spoon-like 

 fashion, however, and the auricles closely resemble the condition of E. 

 hicunter when about 15 mm. in length. 



In Echinometra mathei Blainville, in a young specimen 8 mm. long from 

 Mauritius, the auricles are still separate, but in the adult the auricles are 

 joined in suture and with moderately developed spoon-like processes, but 

 not as high processes as are those in adult E. lucunter. In Heterocentrotus 

 trigonarius (Lamarck), from Mauritius, a young individual 9 mm. in 

 length, has the auricles still separate, but in the adult of this species 

 auricles are arched and united over the ambulacra and with moderately 

 developed spoon-like processes. 



SUMMARY AND CONCLUSIONS. 



Montego Bay, Jamaica, is an excellent locality for studying Echini on 

 account of the number of species there available and the abundance of 

 material. It is an ideal place for a student who wishes to supplement 

 studies on northern species by observations on tropical forms. 



Some 2,878 specimens of regular Echini were collected and studied, but 

 in no case did any specimen show a departure from the typical pentamerous 

 system. This is mentioned as in previous studies it was found that, on 

 the average, completely or partially trimerous, tetramerous, or hexamerous 

 specimens occurred a little oftener than once in a thousand specimens. 



In the " Phylogeny of the Echini," page 91, it is stated that "all the evi- 

 dence goes to show that the full number of oculars that are to become 

 insert are developed early in the life of the individual and apparently later 

 no change in this respect takes place." It was assumed that in Echini 

 specimens of about half the mature size could be accepted as showing the 

 mature characters as regards oculars, and the tables of ocular plate vari- 

 ation, while based principally on adults, were made up on the basis of con- 



