BIH 



ANG TILL K. SV. VET.-AKAD. HANDL. BAND 13. AFD. IV. N:0 5. 97 



departs aborally, and the flve ridges thus formed converge 

 över the middle point of the dorso-central ossicle. 



If, with these features of the Sulenian calyx in view, \ve 

 recall in the Arbacia the idca of its once aproctie calyx,. 

 such as it must have beeu before the remodellinor outbreak 



o 



of the efFerent aperture, homology deraands to see restored, 

 with the central ossicle in its imimpaircd pentagonal ontline, 

 ulso, converging at its middle point, the five ridges emitted 

 from the angles of the heterotropous cpistromal pentagon. 

 The conformity then would becomc complcte. And thus an- 

 other instance wonid present itself of a structure, seen to 

 exist but transientlv durin or tlie earl v stao-c of a recent form, 

 as the Arbacia, being found formeriv to have been constant 

 for life in other not distantly related but mostly extinct forms, 

 as are the Salenia?. And to these it seems to have descended 

 from other forms again, of an an- 

 cestral type and infinitely more 

 remote antiquitv. The succession, 

 witnessed by Paleontology, of the 

 »Echinus spinis mobilibus aculea- 

 tus • to the early Crinoideans, such 

 as the Callicrinus, with its reti- 

 form epistroma rising into inter- 

 sectional acuminate protuberances, 

 recalling those in many Asteriads 

 — and, distantly, the rods of some 

 Plutei, — is seen going on to-day 

 under our eyes during the early 

 individual development of tlic Ar- 

 bacia. If this be so, it may be allowable to surmise the exi- 

 stence of this striking skeletal feature in the Ophiurae also, 

 and pcrhaps even in the Holothurians. It was a wish to obtain 

 some light regarding one of its appearances that drew me into 

 this cursory digression. It is time to leave to others the task 

 of testing the validity of its suggestions and of further prose- 

 cuting its object, and, for me, to revert to the Linnean species. 



The Calyx of the Callicrinus 

 Koniuckianus Ang. From An- 

 GELIN, Iconogr. Crinoideorum. 



The ambitus of the largcst among the specimens of Arba- 

 cia Lixula L., «, Tab. 3, Jig. 1, 2, 3, is verv slightly pent- 

 angular, that of the other three, jig. 4, 5, circular. Vertically 

 the test is hemispha?rical, rounded, the height being in a 0,5.5, 



7 



