STUDIES OF JAMAICA ECHINI 



By Robert Tracy Jackson. 



It was my privilege to join the Carnegie Institution of Washington 

 expedition to Jamaica in the spring of 1912. While there, studies were 

 made of the later stages of development and the variation of a number of 

 species of regular Echini. All the material studied was collected at Montego 

 Bay, close along shore in shallow water of less than a fathom in depth. This 

 locality is very favorable for studying these animals, as abundant material 

 can be obtained, on the reefs or grass-covered bottom, by wading in water 

 usually less than 3 feet in depth. The observations are in extension of those 

 recently published in the " Phylogeny of the Echini " (Memoirs Boston 

 Society of Natural History, vol. 7, 1912). As only a few species are in- 

 volved, they are taken up systematically, giving under each the results of 

 the observations. 



Elxidaris tribuloides (Lamarck). 

 This species is fairly common at Montego Bay, so that sufficient material 

 was available for laboratory work, but it was not so abundant as the other 

 species of regular Echini studied. It occurs in shallow water and is sur- 

 prisingly dull and sluggish, presenting none of the activity of motion seen 

 in Centrechinus or the more passive Tripneustes. In collecting Eucidaris, 

 one simply picks them up, and in no case observed did the animal cling 

 to the ground by its tube-feet. The adults at Montego Bay are rather 

 small for the species, not attaining the size of specimens seen from the 

 Bahamas. An average adult from Montego Bay measures about 30 to 

 35 mm. in diameter. Material from Port Antonio, Jamaica, also is small, 

 but is very abundant, as I had over 500 specimens collected at that locality. 

 Of a limited number of specimens of this species from the Bahamas, the 

 largest noted is 52 mm. in diameter. Only a few young specimens of 

 Eucidaris were found at Montego Bay. In individuals measuring up to 

 10 mm. in diameter the ocular plates are all exsert and the genital pores are 

 wanting. There was not sufificient young material to study the periods at 

 which the ocular plates travel in and reach the periproct. In the adult of 

 this species, typically (58 per cent), oculars V, I, IV are insert, as previously 

 ascertained from an examination of 849 specimens from several localities. 

 A specimen measuring 11 mm. in diameter has all five genital pores in 

 place, as have also all larger specimens. Whether the genital pores would 



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