54 SVEN LOVEN, ECHINOLOGICA. 



the lengtli and the npper parts of tlie wings become separated 

 by a large and deep cleft. In the Cidarids the halves are 

 more massive than in the two Ectobranchiates, and the alveolar 

 cavity less spacious. In the former, also, the aboral trnncated 

 margins of the wings slope inward, &, so as to form with the 

 inner margin a right, or obtuse, angle, while the external 

 angle is acnte; whereas in Echinometra and Asthenosoma the 

 margin of the wing rises inward, thus cansing the inner angle 

 to become acnte, and the external nearly right. 



The pyramid of the Discoidea cy lindrica is mncli broader 

 in proportion to its length than those of the Cidarids or Ecto- 

 branchiates. Their halves have more of the Cidarid. They are 

 upon the whole more massive. The symphysis reaches 0,74 of 

 the whole length, and, conseqnently, the foramen» between the 

 npper parts of the halves is much less deej) than in the other 

 Ectobranchiates, but not fully as shallow as in the Cidaris 

 papillata. The external snrface is not as regnlarly convex as 

 in the Cidaris, but the middle prominence is less marked and 

 less broad than in the EchinidsB, and the depressions on either 

 side of it much slighter, the margins not as thin as in the 

 Echinometra, nor made distinct by a conspicuous furrow as in 

 the Cidaris. The aboral margin of the wing, when seen from 

 the cavity, does not slope inward as much as in the Cidarids, 

 but is far from rising as in the Echinometra or Asthenosoma. 

 The supra-alveolar process is not quite as high as in the Ci- 

 daris, but, seen from the lateral face and from above, it is fully 

 as massive, and somewhat trnncated. The area of the sym- 

 physis is broader than in any genus of the Regularia. The 

 dental slide is somewhat shorter than that area, and the 

 styloid processes of the linCcE eminentes have not been very 

 prominent, Fl. X, fig. 114, 115. The two linefe are very close 

 together, and a canal seems not to have existed. The roughened 

 area, to which the intervening fibrous tissue has been affixed, 

 is distinct. 



It would be of no little interest to learn something more 

 respecting the dental apparatus in the other Echinoconidpe, 

 particularly in the Galerites Albogalerus Leske, whose au- 

 ricles by their stränge reclining posture seem to foreshow con- 

 siderable modifications in the pyramids. The frequent occur- 

 rence of this species in the chalk seems to promise well for a 

 careful search among numerous specimens easily procured. 



