196 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



other cases, even lateral furrows only faintly indicated; ambulacra broad, .S5-.45 

 of interambulacra ; poriferous zones more or less sunken ; median area much broader 

 than a poriferous zone, usually sunken and often bare along middle ; each ambu- 

 lacral plate bears a single secondary tubercle, a little above inner pore, and in 

 addition 1-8 miliary tubercles, between which more or less space is left bare (amount 

 of bare space varies greatly in different species; in tubaria, entire median ambulac- 

 ral area is sunken and bare save for marginal tubercles, while in mikado scarcely 

 any bare spaces are visible ; other species clearly connect these two extremes) ; 

 pores oblique or rarely horizontal; distance between two less than diameter of 

 pore ; surface of interval elevated or roughened. Abactinal system variable, rang- 

 ing from less than .40 to over .50 h. d. Actinostome about equal to abactinal system 

 or smaller. Primary spines very variable, .75-2.00 h.d., always rough, and thorny 

 or prickly ; tips of some usually more or less expanded into a large and conspicuous 

 crown, cup, or even plate, which is often only of a little greater diameter than thick- 

 est part of spine, but may become as much as .50 h.d. ; actinal primaries variable, 

 rough or serrate, usually somewhat flattened ; secondaries thick, of moderate length, 

 more or less flattened, rounded at the end. Tridentate pedicellariae wanting, and 

 large, globiferous ones with no end-tooth on the valves. 



The typical examples of this genus, sucli as tubaria, are very easily recognized, 

 but it is less easy to place such species &s florigera and mikado. Nevertheless the 

 genus is very generally accepted and seems to be a natural group. Mortensen 

 (:03) has made two new genera (Petalocidaris and Schizocidaris) and a new sub- 

 genus (Discocidaris) out of the species here included in Goniocidaris, but none of 

 these rest on anything better than some trifling peculiarity in the large globiferous 

 pedicellariae. Whether we are to find the origin of Goniocidaris in such a form 

 as Phi/llacanthus verticillata may be open to question, but the median ambulacral 

 and interambulacral areas of that species could easily be transformed into those of 

 6. tubaria, while perfectly horizontal pores are found in 67. biserialis. There can 

 be little question, in any case, that the three southern species are closely related 

 to eacli other, and the same is true of the Japanese forms, while florigera seems 

 to be structurally, as well as geographically, intermediate. The genus is appar- 

 ently recent and confined to the southern and western Pacific Ocean. The follow- 

 ing key is based on the examination of 133 specimens, including all of the species, 

 except florigera. 



Key to the Species. 



Each coronal plate with but few (30-70) secondary and miliary tubercles, 



median interambulacral area conspicuously bare and often sunken ; 



median ambulacral area commonly without miliary tubercles, except 



near margin, so that it is often bare and usually much sunken. 



Small (20 mm. or less h. d.) ; coronal plates, 6-8 ; abactinal system about 



.50 h. d. and actinostome nearly equal ; some primaries taper to a 



point, while in many specimens, others, abactinal ones, are abruptly 



and enormously expanded at tip into a plate, diameter of which may 



be .50 h.d.; primaries usually more or less covered, at least near 



base, with a coat of woolly, calcareous hairs . cljjpeata 



