PALEONTOLOGIC CONTRIBUTIONS 



53 



prominently, but because they do not reveal any plated or spinif- 

 erous structure the writer regards them as false characters, pro- 

 duced during the permineralization of the specimen. This con- 

 clusion is further supported by the fact that otherwise the characters 

 are those of S . s a 1 1 e r i . 



The regular outline and development of these interbrachial areas 

 in both specimens suggest already that they are more than acci- 

 dental features. This suspicion is strengthened by the fact that 



Ms- 



Ma 



coe. 



Fig. 21, 22, 23 Diagrams illustrating structure of Auluroidea. 21 Trans- 

 verse section of ray, after Schondorf : A, ambulacral ossicle, Ad, adam- 

 bulacral ossicle ; Wr, interskel'etal radial water vessel ; F, podia, on left the 

 canal passes through the plate, on right, the plate is dissected down to the 

 canal. 22 Ventral arm structure of auluroid, after Schondorf: A, Ambu- 

 lacralia; A', ventral extensions of ambulacralia ; Ad, adambulacralia ; 

 FS, podial cavities. 23 Diagrammatic section of ray of Sten aster 

 obtusus (Forbes) from Spencer, showing dorsal integument, protecting 

 coelom (coe.) : AmCh, ambulacral channel; M, muscles 



they correspond exactly to the narrow basal portions of the 

 petaloid arms (see pi. XI, fig. 1), thus giving them the necessary 

 support. They resemble in this regard the interbrachial areas of 

 the later auluroids with petaloid arms, notably of the species of 

 Encrinaster. Positive proof, however, is furnished of the actual 

 fossil nature of the interbrachial areas by their continuation into a 

 dorsal integument of the starfish. This was fully present in both 

 specimens, but was unfortunately worked away by the writer in One 

 of them before its nature and importance were recognized. 



