OCULAR AND GENITAL PLATES. 113 



species, one specimen, 8%, has ocular I only insert as an arrested variant; of progressive 

 variants, one specimen has oculars I, V, IV insert, two, or 17% have I, V, IV, II, and one has 

 all oculars insert (text-fig. 105). A large series W observations on this species would be 

 most interesting. The wide range of characters of the Saleniidae and the progressive feature 

 of the same, as shown in the table (pp. 156, 157), are striking. 



Of the fossil Phymosomatidae I have only seen the ocular plates of Phymosoma delamarei 

 of the Cretaceous. In ten specimens of this species all the oculars are insert (text-fig. 106), 

 a very unusual IVIesozoic character. In the Recent Glyptocidaris {Phymosoma) crenulare 

 A. Agassiz, Mr. Agassiz (1873, p. 488, Plate 7a, fig. 8) says that two oculars reach the peri- 

 proct. His photographic figure shows only ocular I insert, and the same condition of I insert 

 exists in the only specimen I have seen, therefore apparently one or two oculars may be insert. 

 On the basis of this evidence, ocular I enters the periproct first in the Phymosomatidae as in 

 the Saleniidae, not ocular V as in the Arbaciidae. Additional observations on species of this 

 family would be of much interest. 



The Stomopneustidae of Mortensen with the one species, 

 Stomop7ieusi.es variolaris, was set apart by that author (1903, p. 

 133) as a distinct family. I include the family here as its lan- 

 tern has keeled teeth and epiphyses not meeting across the foramen 

 magnum, thus referring it to the suborder Stirodonta. Other 

 features of the lantern associate it closely with Glyptocidaris as 

 described under consideration of the lantern. In Stomopneustes 

 variolaris (64 specimens) typically, 70 %, oculars I, V are insert 

 (text-fig. 108). In 2%, ocular I only is insert as an arrested 



variant (text-fig. 107), and in 22%, oculars I, V, IV are insert as 



^ & ^' /f^' Text-fiu. 100. — p/()/mosoma de- 

 progressive variants (text-fig. 109). Aberrant variants are 6%, lamard (Desor). Senonian, Les 

 of which one specimen has ocular IV only insert, a very rare Tamaiins, Algiers. Diam. 29 mm. 

 variant in Echini, and three have oculars I, V, II insert (text-fig. ■ ■ ■ o ., t . x . . 



oculars insert. 



110). The occurrence of I, V, II insert is of special interest, as 



this and Acrosalenia hemicidaroides are the only known species in which it has been found ex- 

 cepting in the Echinidae and Strongylocentrotidae, where it is a common character. This 

 with other characters suggests a connection between the families (pp. 186, 214). 



The Arbaciidae present interesting characters as regards ocular plates in their relations 

 to the genitals. Some species are characterized by having all oculars exsert, others by having 

 three plates insert. Those w^hich have most oculars insert are geographically southern species. 

 The order of incoming is V, I, IV, not I, V, IV, and this sequence is characteristic of this family 

 and the Echinometridae (as here restricted) only in the order of the Centrechinoida. This 

 is a striking distinction, and only two cases of I coming in before V were seen in over 2,900 

 Arbaciidae examined, as seen in the table, p. 158. 



