72 SVEN LOVEN, ECHINOLOGICA. 



auricles rising from the anibulacra, in the proloiigatioii of the 

 outer wiiig- of the pyramid and the hgiire of the symphysis 

 area, in the greatly devehjped huinp (jf the corpiis, and in the 

 position and number of the spha'ridia. With Encope and Echi- 

 narachnins it accords in the disposition of its ambulacra which 

 interrupt the sequence of the interradials and give place in the 

 peristome only to a dirainutive first plate, and with the Eclii- 

 nocyamns in the nearl}' vertical position of the ontward cur- 

 ved teeth — but not in their form, — in the shape of the 

 test and the pentagonal tigiire of the whole maxillary system. 

 Bnt from them all it differs by the fossa^ and ))y the form 

 of tlie alveolar ambitus. 



lmj)ortant characters common to all the forms of the tribe 

 indicate a mode of living very diiFerent from that of the Odon- 

 to])hora Regularia. By the more or less flattened form of 

 the test its ventral half-part is brought iiito ample and con- 

 stant eontaet with the gronnd along whieh it is dragged by 

 minute but very numerous pedicels and dense but short and 

 slender spines. The peristome of the young persists in the 

 adult unaltered in composition, the sölitary first interradial plate 

 retains its place, and the primary first plates of the ambu- 

 lacra, not detached from their columns, remain as parts of 

 the final l'orona, eacli with its charaeteristic pore and large 

 pedicel. Aecordingly the membrane that within the stoma 

 surrounds the oral aperture, is labial, and presents no trace of 

 reabsorbed ambulacral jilates. The dental system offers great 

 peculiarity: the bilaterally disposed pyramids, of which the 

 axial 5 always is larger and higher; the total absence of the 

 musculi radiales; the all but universal reduction of the rotula, 

 the rudimentary condition of the epiphyses which in the Re- 

 gularia play so essential a part in supporting the strain ex- 

 erted by the retractors; the teeth feebly and variously arcua- 

 ted, more or less reclining, bilaterally convergent, the axial 5 

 stronger, with the upper angle of its crown nearl}^ right, the 

 front pair, 2 and 3, working upon it, with their u])per angle 

 obtuse, the adoral angle more acute, the 1 and 4 intervening 

 from the sides. The whole is evidently adapted to movements 

 of no great j ^vertical ^amount and essentially horizontal, go- 

 verned Ijy muscles comparatively of no great strength, — inter- 

 pyramidal muscles whose mode of attachment does not point 

 to a habitual strålning of their fibres ; retractors, rather strong, 



