OCfLAIt AND CKMTAI. I'I.\TKS. VI 



as genitals. By a slip of the pen Mr. Agassi/, j,, d,,. paragraph Dinted compare- the live plate, 

 in the dorsal angles of the oculars of Bothrioeidaris to live an:il plate- in young ri.lnri.l-. Tin- 

 five plates in Bothriocidaris (Plate 1, fig. 2) arc interradial in po.-iti.,n and li.- between the 



oculars, whereas the five somewhat similar plates in young cidan.l- t.-xi-fig. (il. /'../ //in.- 



cobosi A. Agassiz, 1904, Plate 13, fig. 5), arc radial in position and lie between the genitals, for 

 the genitals alone reach the periproct, the oculars at tin- Mage in ddarid.- being ev-ert. 



Genital and ocular plates are rare in Palaeozoic types, yet excepting the Erhiimcy-tnida 

 I am able to show them in all families other than the An-haencidaridae and in most genera. 

 After Bothriocidaris just considered, the leading character in the Palaeozoic i- for all the 

 oculars to reach the periproct, and to cover the ambulacra and in part the interambulacru on 

 either side. Also the genitals reach the periproct, arc larger than the ocular.-, and cover the 

 interambulacra in part, but not wholly, because the lateral borders of the interambulacra abut 

 against the next adjacent ocular on either side. This character is shown in Palaeechinu- 

 (Plate 31, fig. 4), Maccoya (Plate 34, fig. 6), Lovenechinus (Plate -li>, lig. <i>. Melonechinu- 

 (Plate 56, fig. 6), Hyattechinus (Plate 25, fig. 5), Lepidcchinus 1 1'late (i:?. fig. 7). and nth. 



In one specimen of Lovenechinus missouriensis (Plate 41, fig. 2) in areas D and F, the 

 oculars are exsert, but in six other specimens of the species, with all ocular- in plan-, all tin- 

 oculars reach the periproct. In Lovenechinus lacazei (text-fig. 243, which I owe to the kindness 

 of Dr. Bather), all the oculars are exsert. In Maccoya intermedia (Plate 33, fig. 1 1 1 one ocular 

 is exsert, four insert; and in Plate 33, fig. 12, all the oculars are exsert. In l.< />i>l, chinu* li-xm Un- 

 tus sp. nov. (Plate 63, figs. 7, 8) the oculars arc all exsert as far as preserved, and the same 

 is true of Meekechinus elegans (Plate 76, fig. 5). These are the only cases of e\-crt ocular- 

 observed in Palaeozoic Echini, and may be fairly considered as forerunners of the dominant 

 character seen in Mesozoic and many Recent regular Echini. 



In the Palaeozoic the oculars of Lepidesthes formosa (Plate 68, fig. 5) have two p<>: 

 Oculars in Lovenechinus missouriensis (Plate 42, fig. 6) show a single pore of small >ixe close 

 to the ventral border of the plates, and the same is seen in Lepiiiu-lihnis t,;ill<itu* (Plate 63, 

 figs. 7, 8). These last two cases are views of the interior, not the exterior of the plates, and it 

 is possible that the pores did not reach the surface, or did not reach it so as to be seen in external 

 view, as is the usual case in Salenia. In all other Palaeozoic Echini seen, the ocular plates are 

 imperforate. Baily (1865b) figured two pores in 1'nliu echinus elegans. His original >[>ccimcn 

 is shown in Plate 29, figs. 3, 6; Plate 31, fig. 4. The specimen does not have any pores in the 

 oculars and Baily's observation was an error, which has proved unfortunate as his figure of 

 the apical disc has been extensively copied. The characters of pores in the genitals and other 

 special features of these plates are considered in the next section. In pn.-t-Palacozoic Echini 

 ocular plates .have one pore not always visible externally (Salenia. Arbacia) and very rarely 

 a second pore may exist as a variant. I have seen only two or three such. 



