45 



,,Diplopodidœ". The biserial arrangement of the poi'es is then evidently ol' no more 

 systematic value than the trigeminate and multigeminate arrangement. It seems 

 to me most correct to make a separate family Micropygidæ, n. fam., lor the genus 

 Micropyga and leave it undecided, whether any of the known fossil genera may 

 he referable to the same family. This family is characterized above all by its 

 anchorshaped spicules, further by wanting ophicephalous pedicellaria- either in the 

 form of true ophicephalous or of claviform ones; the triphyllous pedicellariæ are 

 finely serrate in the outer edge, and the stalk of the pedicellariæ consists of several 

 slender rods, almost not united except at the ends. The tubercles are i)erforate, non- 

 crenulale. The biserial arrangement of the pores and the deep actinal cuts may 

 probably not be family characters; that the extraordinary development of the abac- 

 tinal tubefeet in M. tiiberciilata is no character of high order is proved by the fact 

 that in M. violacea these^tubefeet are simple. 



The arrangement given by Duncan and Gregory of the families (or sub- 

 families) Diadenuitidce and Pedinidce looks most extraordinary. Cœnopedina {Hemi- 

 pcdina) is placed with Centrosteplmniis and Diadema (by Duncan the two former are 

 even regarded as subgenera of Diadema) in the fam. Diadematidœ, Echinothrix and 

 Astropyga (to which Cbœtodiadema and Lissodiadema should probably have been 

 added) in the fam. Pedinidæ. The diagnoses of these two families are: Fam. Diade- 

 matidœ. Ambulacral plates compound near the ambitus, the pairs of pores in 

 simple vertical series or in arcs of three (or more). Fam. Pedinidce. Ambulacral 

 plates compound and the pore-pairs triserial. — I wonder if anybody can find 

 in these diagnoses a single feature , which really ditferentiates these two fami- 

 lies! When reviewing the characters found in the recent genera, Diadema, 

 Astropyga, Cbœtodiadema, Ecbinotbrix, Lissodiadema, Centrostepbanus and Cœnopedina, 

 we find that Lissodiadema and Cœnopedina have perforate, noncrenulate tubercles 

 and smooth spines (solid in Cœnopedina), whereas the other genera have perforate, 

 crenulate tubercles and verticillate (hollow) spines. The spicules are simple, tri- 

 radiate bodies, or larger, irregular, fenestrated plates (Diadema Savignyi. Ecbinotbrix 

 diadema and Cœnopedina). In the two latter a few bihamate spicules may be found, 

 but, though of great interest, this feature can certainly not be of any classificatory 

 value. With regard to the pedicellariæ there are some facts of importance to note. 

 The tridentate pedicellariæ do not present any features of more than specific im- 

 portance; in the triphyllous pedicellariæ it is to be noticed that the edge is smooth 

 and the blade open, without coverplate. The ophicephalous pedicellariæ occur in 

 Astropyga and Cbœtodiadema only in the form of claviform pedicellariæ, seldom 

 [Cbœtodiadema) with the head developed. In Diadema (antillarum) and Ecbinotbrix 

 they occur both as claviform and as true" ophicephalous pedicellariæ, with the head 

 placed directly, without neck, on the stalk. In Centrostepbanus they also occur in 

 both forms, but there is a well developed neck on the true ophicephalous ones, 

 and in the claviform ones the head is especially developed with teeth on the valves, 



