'56 PEOF. p. M. Duncan's eetision op the 



III. Eamily ASPIDODIADEMATIDJE. 



Diadematoidea with spheroidal tests, haying a large, narrow, 

 ringed apical system formed by broad basals and broad inter- 

 vening radial plates ; having few interradial plates, each with a 

 large primary perforate and crenulate tubercle ; straight ambu- 

 lacra with numerous low primary plates with or without primary 

 tubercles ; pairs of pores, one in each plate in straight vertical 

 series. Peristome incised ; branchia; bidd, and with ten very 

 large buccal plates ; tentacles heteropodous. Spines hollow and 

 striated, verticillate. 



The generic definition given by A. Agassiz of Aspidodiadema 

 is very comparative, and we therefore venture to give a positive 

 diagnosis founded upon the study of the species which have been 

 so admirably described and figured in the Reports on the ' Ciial- 

 lenger ' and ' Blake ' Echinoidea *. 



Grenus Aspidodiadema, A. Agassiz, 1879, Proc. Amer. Acad. 

 vol. xiv. p. 199 ; 1881, Report on ' Challenger ' Echini, p. 64 ; 

 1883, Beport on ' JBlahe ' Echini, p. 24. 



Syn. JPlesiodiadema, Pomel, 1883, non Duncan. (Adapted.) 



Test moderately large, tall, spheroidal, thin ; interradial coronal 

 plates few in number. 



Apical system large, the narrow ring of plates composed of 

 broad basals and of wide intervening included radial plates ; the 

 periproct large, the membrane with few or numerous radiating 

 plates, some united, and. reaching from the ring to the anus, which 

 may be tubular. 



. Ambulacra broad, with a few large primary perforated and 

 Granulated tubercles sometimes reaching above the ambitus, and 

 with smaller tubercles or granules abactinally, or with only small 

 tubercles and loose granules throughout. The pairs of pores are 

 numerous, in simple vertical series, and the plates are simple and 

 low broad primaries. Tentacles heteropodous. 



The interradia have two vertical rows of large primary perfo- 



* The fact that A. microtuberctolatum, A. Ag., has email tubercles on its 

 ambulacra must not be forgotten ; but at the same time it must be remembered 

 that all the other generic characters are the same as those of the other species. 

 It id hardly worth while, therefore, to disturb the genus, as has been attempted 

 by a naturalist who has not seen the forms. 



