44 NEW YORK STATE MUSEUM 



eight rays, but the larger may have possessed nine. The number of 

 the rays may therefore have been somewhat variable or rather 

 increased somewhat with growth, as it still does today in multi- 

 radiate forms. While Lepidaster with thirteen rays is a Silurian 

 type, Helianthaster, Lepidasterella and Lepidasterina are Devonian 

 forms, Helianthaster with fourteen to sixteen rays early Devonian, 

 and Lepidasterella and Lepidasterina late Devonian. Lepidasterina 

 has less rays than any of the others and contrasts especially with 

 Lepidasterella, which has more than the preceding genera. While, 

 therefore, an increase in the number of rays seems to have taken 

 place in one direction, a decrease seems to have led to Lepidasterina. 

 If, as has been suggested, the increase in the number of arms has 

 been principally to permit to gain a stronger hold on the food 

 and on the rocks, then Lepidasterina would appear to have made 

 up for the smaller number by increased relative length of the rays 

 in comparison with the size of the disk. It is just the opposite in 

 relative size of rays and disk to Lepidasterella. 



Ptilonaster princeps Hall 



Plate 20, figure i 



The genus Ptilonaster, with its genoholotype P. princeps, 

 is based on a single specimen from the " Chemung group at Cort- 

 landville," (now Cortland), N. Y., which is now in the American 

 Museum of Natural History. The specimen consists, according to 

 Hall's statement, of the impression of the greater part of one ray, 

 with parts of two others, and intervening portions of the disk. 

 The State Museum contains original wax and plaster casts and 

 replicas of the ray, figured by Hall. These show that the original 

 drawing of the species (20th Ann. Rep't, N. Y. State Museum of 

 Nat. Hist., pi. 9, fig. 9, 1867) is a diagrammatic one, intended to 

 indicate the outlines of the ossicles as understood by Hall. Based 

 on the original description and this figure, the genus has always 

 remained problematic in regard to its taxonomic position, and 

 authors, as Gregory and Schuchert, have been satisfied with leaving 

 the genus next to Eugaster where Hall had placed it. If we, with 

 the same incomplete material as was available to Hall, venture 

 to suggest a different position for this genus, it is mainly because 

 we have before us other genera still more similar to Ptilonaster and 

 not known at the time of the creation of the genus. 



As Hall gives but the diagrammatic drawing of the ossicles 

 which fails to record the actual aspect of the actinal side, we repro- 

 duce here the wax cast of the type from which the original drawing 



