CLARK: THE CIDARIDAE. 223 



in contact with anal plates except right anterior one ; this ocular is wholly or very 

 nearly excluded ; instead of being an individual peculiarity (as sometimes occurs 

 in Tretocidaris et aL), this curious arrangement is remarkably constant, and is as 

 evident in a specimen 17 mm. h. d. as in those over 40 mm. Actinostome .35- 

 .40 h. d., generally about .90 of abactinal system. Primary spines unique, 2.5- 

 3.3 h. d., straight or somewhat curved, nearly smooth ; base broad and depressed, 

 somewhat triangular in cross-section, with more or less evident traces of longitudi- 

 nal series of granules, but in large specimens these are scarcely visible ; collar 

 enormously wide, .20 or more of length of spine, and abruptly contrasted with 

 remainder in color ; this remainder bears 10-20 sharply distinct longitudinal ribs, 

 which are seemingly continuations of series of granules on collar; outer limit of 

 collar not straight, i. e. forming a ring around spine, but more or less deeply 

 concave on both sides, especially actinally ; tip of primary blunt or more or less 

 expanded ; actinal primaries conspicuously capped and serrate as in Stephanoci- 

 daris, but much stouter than in that genus ; secondaries long, slender, and flat. All 

 three kinds of pedicellariae present; globiferous, both large and small, lack an end- 

 tooth on valves ; stalks of large ones usually with a " limb." 



This notable genus will be recognized at first sight by the peculiar, handsome 

 spines somewhat resembling those of Coelopleurus. The above diagnosis is based 

 upon the examination of fifty fine specimens of hastigera, representing all ages. 

 The type of the genus is the species named by Bell ('93) curvatispinis, but nothing 

 is known of its test or abactinal system, for neither Bell nor Mortensen (: 03) 

 has attempted any description beyond spines and pedicellariae. It is interesting 

 to find that the " Siboga " collected in the East Indies a third species of this 

 genus, which de Meijere ( : 04) has named Cidaris maculicollis. His careful de- 

 scription of the primary spines leaves no doubt as to the proper relationship of 

 this new form, although the describer, in spite of the primaries, places it in the 

 same subgenus with C. metularia, tribuloides, etc., because he considers the large 

 globiferous pedicellariae like those of Cidaris. As a matter of fact, however, the 

 valve of a pedicellaria which de Meijere figures is quite as near Acanthocidaris as 

 it is to typical Cidaris. On account of the broad collar and the serrate actinal 

 primaries, de Meijere (: 03) originally described maculicollis as a Porocidaris, 

 but it really has as little in common with that genus as with Cidaris. 



Key to the Species. 



Collar of primary spines very light-colored, unspotted ; remainder of spine 

 reddish or brownish. 

 Secondaries cream-color or yellowish ; base of primaries with distinct 



angles, which may be somewhat serrate curvatispinis 



Secondaries dark reddish-brown ; base of primaries with rounded angles, 



not in the least serrate hastigera 



Collar of primary spines greenish, with red spots ; remainder of spine whit- 

 ish with 3 or 4 cross-bands of reddish maculicollis 



