Studies of Jamaica Echini. 



155 



variants with oculars V, I insert. The percentage of V insert at this age is 

 quite near that of the next larger series, but there are more arrested and fewer 

 progressive variants than in the older series. The series 40 to 52 mm. in 

 length, 103 specimens, includes the largest specimens collected at Montego 

 Bay. From other localities specimens may attain a length of 90 or more 

 millimeters. Of this series, 7 per cent have all oculars exsert as arrested 

 variants ; 66 per cent have ocular V insert as the maximum development of 

 the species character in the locality; 26 per cent have oculars V, I insert as 

 progressive variants. One specimen, i per cent, has oculars V, II insert 

 as an aberrant variant, and this was the only aberrant found in the whole 

 series of 503 specimens collected at Montego Bay. 



Considering the ocular arrangement of Echinometra lucunter at Montego 

 Bay as a whole: It is a desirable type to study because its species character 

 is to have one ocular insert, and this is a very unusual feature in Echini, 

 otherwise occurring only in the recent Saleniidae and in Echinus magel- 

 lanicus Philippi from South America. Other Echini, both recent and 

 fossil, are characterized as the species feature of adults by having all oculars 

 exsert, or two oculars insert, or three or more insert, usually three or five. 

 Five insert is a not unusual feature in both living and fossil types as 

 far back as the Palaeozoic. In Echinometra lucunter it is seen that oculars 

 are all exsert up to a comparatively large size, 15 mm., after which oculars 

 travel in gradually with increasing size, the highest percentages of insertness 

 being in full-grown specimens. Comparing the present tabulation of this 

 species with that previously published (Phylogeny of the Echini, p. 163), 

 it is seen in both that ocular V insert is the species character, though in 

 Bermuda material oculars V, I insert is nearly as frequent. In both lots 

 ocular I insert is a rare feature, and aberrant ocular arrangement is rare. 

 As material previously tabulated was not graded by size, no comparison 

 can be made in this respect. 



18 



Figs. 18-21. — Development of the perignathic girdle in Echinometra lucunter (Linne). 

 Fig. 18. — Young specimen from Montego Bay. Jamaica. Specimen s mm. long. Auricles are erect separate 



styles. 

 Fig. 19. — The same. Specimen 8 mm. long. Auricles arched over the ambulacrum but separate, apophyses 



developing. 

 Fig. 20. — The same. Specimen 15 mm. long. Auricles joined in suture over the ambulacrum. 

 Fig. 21. — Large adult from Bermuda. Specimen 6s mm. long. Auricles produced vertically as high spoon-like 



plates, apophyses high ridges. 



The teeth of Echinometra lucunter extend horizontally over the top of 

 the lantern and the proximal end of the tooth is bent back on itself and in 

 the same plane, as previously described in Strongylocentrotus. The proximal 

 part of the tooth is grooved, the keel developing as one passes adorally; 



