.") I III l.l.KTIN 82, UNITED STATES NATIONAL MUSEUM 



of the dorsal coelome. The youngest representatives have numerous small cirrus 

 sockets without sculpture, in alternating rows, concealed basals, ao tree dorsal margin 

 of the radials, and a fairly small radial cavitj ; the radial pits are -hallow or obliterated. 



;i observed a rosette in Semiometra impressa. He said that t lie recent form 

 nmu may properly be included in this series, as it is undoubtedly nearly related 

 to Lonolometra, from which ii differs in its shallower and wider radial coelome pits, by 

 having a relatively larger centrodorsal cavity and, in full grown individuals, by the 

 absence of sculpture on its cirrus sockets. The later forms of this series advance to- 

 ward group a of the Macrophreata (see Part 3, page 63, under Macrophreata). The 

 'roup with its line radial pores corresponds as regards this character to the 

 family Ajsterometridae in which the radial pits are deep, but very narrow. 



The conometrid series, relatively poorly represented among species in which the 

 radial pentagon is known by the genera Amphorometra, Placometra, Conometra, and 



elametra, is more numerously represented within the genus Olenotremites by the 

 anglesensis and peUoti groups. This series is distinguished from the preceding one 

 by the t b ence of radial coelomic pits. Among recent forms it has its analogy in the 

 Thalassometrida, •-■< nsv, stricto. 



Gislen said it is very remarkable what a large number of species id' which only the 

 centrodorsal is known are found iii both these series, contrasting with the conditions 

 ;n the solanocrinid series. ]n the genus Olenotremites of the solanocrinid type only 

 live species are found (the exilic group). But there are 30 species that can certainly 



icluded in the two -cries now under discussion. This is due in the case last men- 

 tioned to the fact that the elements of the radial pentagon are loosely connected both 

 with each other and with the centrodorsal. In the recent Thalassometrida the corre- 

 sponding ossicles very soon fall apart when boiled in caustic potash. A feature to be 

 noticed is that in the recent Marianietrida the centrodorsal and the radial pentagon 

 are very firmly united with each other, exactly as appears to have been the case in the 

 d Bolanocrinids. 



It seemed scarcely probable to Gislen that the notocrinids could have descended 

 from any of the comasterids or solanocrinids. In the last named, to be sure, we some- 

 times find diverticula from the dorsal coelome between the centrodorsal and the 

 radial pentagon, indicated by shallow branched meandering furrows. These, how- 

 ever, are entirely different from the deep and broad perpendicularly penetrating pits 

 which occur in Loriolointtnt. I of their depth — they traverse almost the whole 



of the centrodorsal even in full-grown individuals it is easj to assume their pro- 

 longation into the stein in stalked young. 



Although there are a good many similarities in regard to general feature- between 

 Archoeometro. and Amphorometra, Gislen said it is not very probable that the cono- 

 metrid- are deii\ i:\ from either of the two families first mentioned. This is made still 

 lees likely by the fact that in the I'pper Jurassic we meet with a form which it seems 



it fairly well he considered a primitive ancestral form of the Thala--oinet rida and 

 Conometridae in general, and of Placometra in particular. 



Gislen -aid we therefore reach the conclusion in these two cases also that these 

 two families possibly represent one. or perhaps two, special offshoots from the 



pentacrinid stock, w huh in that case have attained the coinatiilid type by independent 



path- 



