64 SVEN LOVEN, ECHINOLOGICA. 



pyramid. Seen from above, the pyramid has tlie form of an 

 arrowhead, fig. 75, with the sides iiearly straight and the 

 external angle reentering deeply between the elongated, tape- 

 ring wings. The snpra-alveolar crest, er., which in the Cly- 

 peaster is transverse, here arises on either half-pyramid with 

 one of two elevated diverging branches that terminate each 

 in a broad snpra-alveolar process bearing at its lateral detrun- 

 cated end the minnte and very thin and low, lameliar epi- 

 physis, fig. 73, 75. The exceptional form of the rotnia, fig. 

 73, 77 a, h, was remarked by Johannes Muller. Its lower 

 part, contained between the epiphj^ses, is compressed, the np- 

 per snrface has a ronnded knob, and the expanded margins 

 are nneqnally bilobate, the larger lobe, one of the two inner 

 ones, being directed, symmetrically, in I and V towards the 

 longitndinal axis, in II and IV likewise, and forwards, in III, 

 towards the II. The lower snrface of the pyramid, fig. 76, is 

 concave, the mesial sntural ridge strong and accompanied on 

 either side by another elevated line; the lameilar fringe is 

 narrow; there are no excavations for the auricles. The labial 

 process is large and prominent. The sides of the pyramid, 

 fig. 73, the inter-muscnlar sheets, are very long, lanceolate,^ 

 the rachis produced, fig. 74; the series of larger holes conspi- 

 cuons, bnt the radiating ribs obscnre and imperforate. The 

 triangle, tr. fig. 73, is well marked, broad at the epiphysis, 

 and smooth. The inner wing is ver}^ short, and nearly devoid 

 of lameliar partitions. The anricles, see woodcnt p. 73, are small; 

 they arise from the ambnlacra, very close together, even conti- 

 gnons, the iirst interradial plate being always very minute,^ 

 of ten snppressed. The retractor muscles, m. re. fig. 73, are 

 horizontal, their horseshoe-shaped attachment being nnder the 

 crest of the anricles, their insertions on either side of the sn- 

 tural ridge in a hollow under the base of the prominent la- 

 bial process, fig. 76. The very slender protractor muscles m, 

 pro., are attached on the auricles close together at the junc- 

 tion line of these, between the retractors, and ascend right 

 npwards, being inserted on either side of the mesial ridge 

 at its outer third part. The teeth, VI. VIII, fig. 73, 74, 

 78, Pl. XI, fig. 146, are long, very slightly curved inward, 

 high, compressed, thickened adorally; the 5 much the larger, 

 not far from right- angled at the crown end. 

 > Etudes, Pl. LI, fig. 247— 2r)0. 



