Studies of Jamaica Echini. 149 



joined in an arch over the ambulacral areas. In large adults the apophyses 

 are developed as a moderate ridge and auricles are joined in a delicate arch 

 which never becomes heavy, as in large specimens of Tripneustes. 



Tripneustes esculentus (Leske). 



One of the abundant species at Montego Bay is Tripneustes esculentus 

 (Leske). It occurs on grass bottom and also on the reefs in shoal water, 

 and is a strikingly handsome sea-urchin when alive, with its white spines 

 against the dark purplish groundwork of the fleshy covering of the test. 

 The larger individuals live out in the open in full view, but young specimens 

 are found only in crevices or on the under side of rocks. The young are 

 not common, and although sought for diligently, no very young specimens 

 were found and only a limited number of the youngest seen were obtained. 

 Perhaps some other time of year, as summer or autumn, would be more 

 favorable for young material of this species. In Tripneustes esculentus from 

 this locality the ocular plates continued to travel in or enter the periproct, 

 from the youngest to the largest series of specimens observed, as shown by 

 the tabulation. For this reason, as regards the feature of ocular plate 

 development, what is called the developing series for this species in the table 

 is arbitrarily drawn at a maximum of 70 mm. 



Taking up the developing series: Ten specimens of 20 to 25 mm. diam- 

 eter have 50 per cent with ocular I only insert, and 50 per cent with oculars 

 I , V insert. Younger specimens would doubtless have all oculars exsert as a 

 developing stage. The next size, 25 to 30 mm. diameter, 21 specimens, 

 has 24 per cent with ocular I only insert and 76 per cent with I, V insert. 

 The relations of these two younger series shows that it is a period of rapid 

 development. The next series, 30 to 40 mm. diameter, 60 specimens, has 

 12 percent with I only insert; 80 per cent with I, V insert; 2 per cent with 

 I, V, IV and 2 per cent with I, V, IV, II insert. Three specimens, 5 per cent, 

 are aberrant with I, V, II insert. This stage, while holding the I only insert 

 as a developing character, has attained the I, V; the I, V, IV; and the I, V, 

 IV, 1 1 insert ; which are each respectively the feature of the species as a 

 character in one or more of the several localities from which material was 

 studied, but the relative proportions of the three characters differ from 

 that of any known adult series. 



The series 40 to 50 mm. diameter, 42 specimens, has lost the I insert as 

 a youthful character; 90 per cent have oculars I, V insert; 2 per cent have 

 I, V, IV, and 2 per cent have I, V, IV, II insert. Five per cent are aberrant, 

 one of the two specimens having I, V, II insert and the other V, II insert. This 

 stage has the highest percentage of I, V insert of any age of material from 

 Montego Bay. The series 50 to 70 mm. diameter, 34 specimens, has 53 

 per cent with oculars I, V insert; 18 per cent with I, V, IV; and 6 per cent 

 with I, V, IV, II insert. Aberrants are 24 per cent, eight specimens, all of 

 which have oculars I, V, II insert. The developing series in its later phases 

 may be compared broadly with material from Bermuda or other localities 



