1885.] NATURAL SCIENCES OF PHILADELPHIA. 319 



smaller than any of the Canadian species. It has but one sec- 

 ondary radial, and fewer and larger interradials both dorsally 

 and ventrally, but otherwise agrees well with those types. It 

 probably represents paleontologically a younger stage of that 

 genus, for the arms are free from the first secondary radial. In 

 Lyriocrinus the arms proceed upward in a straight line with the 

 walls of the calyx, the arm openings are located ventrally and 

 are arranged at nearly equal distances from each other; while 

 in Archeeocrinus sculptus the arms extend out laterally in the 

 form of free appendages. In the former the interradials of the 

 ventral side rest against the inner edges of the dorsal cup, the 

 so-called "vault " being perfectly flat; in the latter the.vault is 

 elevated and the interradials along the ventral side are so closely 

 intermingled with the dorsal ones, that no dividing line can be 

 distinguished. 



In Archeeocrinus dexideratus, which is a good t}-pical form of 

 the genus, there are twenty or more interradials beneath the hori- 

 zon of the arms, and these are succeeded by a much larger num- 

 ber of minute pieces at the ventral side, all of which, from the 

 basals up, decrease in size to the oral pole. There are no large 

 plates to represent the proximal dome plates, and hence no orals 

 if these were represented by the proximals as contended by Car- 

 penter. The interradial and interaxillary spaces in the dome are 

 depressed, thereby producing along the surface somewhat irregu- 

 lar ridges, which follow the direction of the subtegminal ambu- 

 lacral tubes. 



The depressed globular form and the wide interradial spaces 

 of the calyx are characteristic features of A rch aeocrinus, which 

 distinguish it readily from all other Silurian Rhodocrinidae. 



Some of our specimens of Archeeocrinus sculptus have beneath 

 the first interradial plate, resting upon the basals, two small 

 additional plates. As these are present only in the larger speci- 

 mens, and totally absent in the smaller ones, in some of them 

 developed in a most rudimentary way, sometimes only in one or 

 two of their rays, it is evident that the}' are the result of extrav- 

 agant growth, and not true interradial plates. They seem to us 

 equivalents of the small accessory pieces between basals and 

 radials in Acrocrinus, in which they attain a much more profuse 

 development, occupying the greater part of the calyx. 



We note here the following additional species : 



