H. L. Haxvlcins — Echinoidea Holectyjyoida. 395 



so that I hereby establish the new genus Apatojjygus,^ whose geno- 

 type and only known species is Nudeolites recens Milne Edwards, 

 1836. A detailed diagnosis of the genus concludes this section of 

 the paper. 



The description of Afatopygus recens (sub Echinohrissus) given 

 by A. Agassiz {Revision, pp. 556-7) is sujfficiently full and in 

 agreement with the specimen before me to serve with but little 

 comment. The description of the peristome and its surroundings 

 is accurate, but Agassiz' use of the term " phyllode " might prove 

 misleading. There is no more trace of phyllodal qualities, whether 

 of plating or pore-disposition, in the orad parts of the ambulacra 

 than occurs in an ordinary Spatangid. The proximal pores are 

 appreciably larger than the others, and tend to perforate their 

 ambulacrals in the median line rather than near the adradial sutures ; 

 but the pores show less tendency towards triserial arrangement 

 near the peristome than on the rest of the adoral surface, while the 

 plating is almost perfectly simple and " Cidaroid " in the region where 

 the jjores increase in size. With regard to the interambulacral 

 parts of the peristome-margin, there can be no doubt that Agassiz' 

 remark that " no buccal bourrelet had been developed " is an 

 under-statement. As far as such a condition is conceivable it may 

 be said that " bourrelets " are positively absent — the proximal 

 interambulacrals are exceptionally thin in their invaginated parts, 

 resembling those of EcJiinoneus more than those of any other recent 

 Echincid with which I am acquainted, and exceeding them in 

 delicacy. The quality expressed in the generic description (loc. cit., 

 p. 556) " Floscelle rudimentary ; no well-marked bourrelets " 

 would, to my mind, be better abbreviated to the bare statement 

 " no floscelle ". 



The nature of the ambulacral plating, which is roughly indicated 

 in Agassiz' figures, but not mentioned in the text, seems to me to 

 provide the most unusual and distinctive feature in A. recens. 

 Analyses of one of the longest areas (I) and the shortest area (III) 

 are here given (Plate VII, Figs. 1 and 2). As far as indications go, 

 area II (which is almost midway between the extremes in point of 

 length) resembles the latter more closely than the former. In all 

 ambulacra, practically the entire extent of the adoral parts (excluding 

 the peristomial portions above mentioned) display typically 

 " Pyrinid " plating (see Hawkins, Phil. Trans., 1920), the demi- 

 plates often undergoing great reduction. In area I this condition 

 ceases just below the ambitus, and the adapical part of the area is 

 built of simple primaries, some of which (below the petals) may be 

 almost half as high as broad. The petal consists of thirty plates 

 in each column, perforated by dissimilar pore-pairs. In area III, 

 Pyrinid structure persists up to, and even into, the petaloid region 

 with characters indistinguishable from those present adorally. 



^ airardoi, I deceive, and -pygiis, normal sufiix for genera of this group. 



