SPECIAL CHARACTKUS OF (JKXITAI. 1'I.ATKS. 



Hi.-, 



SPECIAL CHARACTERS OF GENITAL PLATES. 



Certain characters of genital plates are here taken up aside from th.-ir n-hti,,,,, .,, .! 

 oculars, that have just been considered. The characters in genitals are subject to a great deal 

 of variation. While the bearing of these variations is often obscure, for thr most part th.-y 

 follow very definite lines. In my studies of post-Palaeozoic fossil and H.-m.t Echini, over 



TEXT-FIGS. 177-184. Showing genital plates excluded from the periproct. 



177. Gymnechinus pulchellus Mortensen. Gulf of Siam. Diam. 15 mm. R. T. J. Coll., 863. X 8.2. Genital 3 

 exsert by the contact of genitals 2 and 4. Oculars I, II insert, the species character (pp. 93, 120). 



178. The same. Diam. 10 mm. R. T. J. Coll., 864. X 8.7. Genital 4 exsert by the contact of genitals 3 and 5. 



179. Gymnechinus robittardi (Loriol). Mauritius? Diam. 26 mm. R. T. J. Coll., 811. X 4.5. Genital 3 exsert. 

 Oculars I, II insert, the species character (p. 120). 



180. Strongylocentrotus drobachiensis (O.F. Muller). York Harbor, Maine. Diam. 44 mm. R. T. J. Coll., 782. X 2.81. 

 Genital 3 exsert by the contact of genitals 2 and 4, as in text-figs. 177, 179, 184. 



181. The same. Chelsea Beach, Massachusetts. Diam. 3 mm. R. T. J. Coll., 880. X 28. Genital 4 exsert by 

 the contact of genitals 3 and 5 as in text-fig. 178. No genital pores (compare text-fig. 133, p. 129). 



182. The same. Dumpling Island, North Haven, Maine. Diam. 50 mm. R. T. J. Coll., 866. X 2.7. Genital 4 

 exsert by the contact of genital 5 and ocular IV (compare text-fig. 144, p. 134). 



183. The same. Calderwood Island, Maine. Diam. 32 mm. R. T. J. Coll., 865. X 2. 8. Genital 4 exsert by the 

 contact of genital 3 and ocular V. 



184. Toxopneustes variegaius (Lamarck). Boca Ceiga Bay, Florida. Diam. 58 mm. R. T. J. Coll., 872. X 3.7. 

 Genital 3 exsert (p. 121). 



