Studies of Jamaica Echini. 153 



sive variants than Bermuda material, hence it is structurally an advance 

 on that and a step towards the next higher advance as represented in the 

 series from the Bahamas. 



Material from the Bahamas collected by C. J. Maynard has only 22 per 

 cent of I , V insert. This is not the character of the locality and has therefore 

 passed into the phase of an arrested variant. There are 46 per cent with 

 oculars I,V, IV insert. This is the dominant character of the Bahama mate- 

 rial, while it would be a progressive variant for Bermuda and Florida, and 

 further, would be an arrested variant for the Montego Bay series. In the 

 Bahamas, 27 per cent have I, V, IV, II insert, a common progressive variant, 

 and 2 per cent have all oculars insert. The aberrants are relatively few, 

 3 per cent, four of the aberrants having I, V, II insert and one having 

 I, V, IV, III insert. Structurally, in its percentages of ocular arrangement, 

 the Bahama material is intermediate between the Florida and Montego Bay 

 series. 



The Montego Bay material, considering only the two largest-sized series 

 tabulated on page 156 and treating them as a single series of 90 to 132 mm. 

 diameter, has 19 per cent with oculars I, V insert as a moderately common 

 arrested variant, but with the lowest percentage of any of the localities 

 given. In 24 per cent oculars I, V, IV are insert, which, for this locality, is an 

 arrested variant, though it is a progressive variant for Bermuda and Florida, 

 and a dominant character for the Bahamas. In 40 per cent, oculars I, V, 

 IV, II are insert, the dominant character for this locality, though it is a 

 progressive variant for all the other localities; 3 per cent have all the 

 oculars insert, which as a progressive variant, is only a slight advance on 

 that existing in the other regions cited. The aberrants, 13 per cent, have 

 already been considered above, and do not need further mention excepting 

 that it is interesting that most of them are cases of I, V, II insert, as in other 

 localities. 



In all the localities given Tripneustes esculentus is an abundant form, 

 and in all attains a large size. The specimens from Bermuda were collected 

 for me and averaged very large, the largest measuring 145 mm. in diameter, 

 yet this locality has the lowest ocular index. The cause of the progressiv^e 

 evolutionary series as marked by the higher and higher percentages of ocular 

 plates reaching the periproct is unknown, but it is a fact that it exists and 

 points to the desirability of studying large series of specimens from different 

 localities. 



In Tripneustes esculentus, when opened alive, it is seen that the teeth 

 extend above the top of the lantern and horizontally over the top of the 

 same. The proximal end of the tooth is curved back on itself and is grooved, 

 the keeled character developing as one passes orally along the tooth. The 

 dental capsules are relatively large, all this structure coinciding with that 

 previously described in Strongylocentrotus drobachiensis. In a young 

 specimen of Tripneustes, 24 mm. in diameter, the auricles are slender, but 

 already meet in an arch over the ambulacra. In large adults the auricles 



