OCULAR AND GENITAI, I'l.ATKS. 



Ill 



range of characters as regards oculars, from all exsert, the Jurassic and youthful rhararter, to 

 all insert, and finally oculars and genitals separated by an interspace, a condition <><-eurriiiK 

 typically in no other regular Echini. The oculars reach the periproct in tin- >e<|iienee I, V. IV. 

 II, III, whereas in the two other suborders a different sequence occurs in two of the families, 

 the Arbaciidae and Echinometridae, in which the sequence is V, I and not I, V (WH- table-.. 

 Considering the next suborder, the Stirodonta, we find in the Salcniidac the Mesozoic 

 species of Peltastes have all oculars exsert (127 specimens), as in Peltastes wrighli (Plate 4, fig. 7). 

 In Salenia scutigera (16 specimens) also all oculars are exsert, the same character being seen 

 in many other. Cretaceous species of the genus. In the Cretaceous Salenia petalifera (20 speci- 

 mens) the oculars are all exsert in 95%, but in one specimen, 5%, ocular I is insert as a progres- 

 sive variant, in this feature being like the typical character of Recent species of the family. 

 Of many other species of Cretaceous Salenias seen, but not tabulated, all had the oculars exsert 

 excepting one specimen of Salenia clarki (?) Forbes, in the Jermyn St. Museum, in which ocular 

 I was insert. 



102 



105 



TEXT-FIGS. 102-105. Ocular arrangement in the Saleniidae (pp. 174, 175). 



102. Salenocidaris profundi (Duncan). North of Tristan da Cunha, 1,425 fath. Diam. 10 mm. 

 667. X 4. Ocular I insert, the typical character; the suranal plate is dorsal to genital 3. 



103. Acrosalenia sjnnosa^saiz. Cornbrash, Chippenham, England. Diam. 14 mm. 

 I, V insert, the typical character; the suranal plate is dorsal to ocular III. 



104. Acrosalenia hemicidarMes Wright. Forest Marble, near Malmsbury, England. 

 735 X 8 Oculars I, V insert, the typical character; the suranal plate is dorsal to genital :i 



105. Acrosalenia mltoni Wright. Bradford Clay, near Cirencester, England. 

 X 8. All oculars insert, a progressive variant; the suranal plate is dorsal to ocular II 



The Recent species are very interesting in comparison. As Mr. Agassi* >hmv> 

 Plate 21 fig. 2), in the young of Saknocidaris varispina, all the oculars are eni M in : 

 of Cretaceous species. Of adult Saknia patkrsoni in 16 specimens, 003 

 and 31% are arrested variants with all oculars exsert, like the character of 



