NARRATIVE OF THE CRUISE. 385 



confined to the colder regions of the southern hemisphere, although two of the species 

 extend as far to the northward as the East Indies and Natal. 



"This species (fig. 141) has a general resemblance at a first glance to the small 

 Mediterranean variety (afflnis) of Cidaris papillata, 1 but the radioles are thinner and 

 much shorter, and differ wholly in their sculpture ; the shell is even more depressed ; the 

 secondary tubercles are more distant; and a very regular series of short club-shaped rays 

 seated on miliary granules are interposed in the rows between the spines of the second 

 order. The ovarial openings are extremely minute, and are placed close to the outer 

 edge of the ovarial plates. The upper part of the test is quite flat, the flat space includ- 

 ing not only the ovarial plates and the plates of the periproct, but the first pair, at least, 

 of the plates of each interambulacral area. Articulated to the primary tubercles of these 



Fig. Ul.—Omioeidaris canaliculate, A. Agassiz. Stanley Harbour, Falkland Islands. Twice the natural size. 



latter are two circles of radioles, the inner more slender and shorter, the outer stouter and 



longer, but both series much larger than radioles usually are in that position on the test. 



" These special spines are cylindrical, and nearly smooth, and they lean over towards 



the anal opening, and form an open tent for the protection of the young, as in Cidaris 



/tutrix, a species presently to be described, but at the opposite pole of the body. In this 



species the eggs are extruded directly into the marsupium ; and I imagine, from the very 



small size of the ovarial openings, that when they enter it, they are very minute, 



and probably unimpregnated. In the examples which we dredged at the Falkland 



Islands, the young were, in almost every case, nearly ready to leave the marsupium ; we 



were too late in the season to see the earlier stages, young in the same marsupium are 



nearly all of an age, some somewhat more advanced than others. The diameter of the 



test is from 1 to 1*5 mm., and the height about 0*8 mm. ; the length of the primary spines 



1 DorotddarU papillata of A. Agassiz. 

 (nauh. uiall. exp. — vol.. i. — 1884.) 49 



