212 PROCEEDINGS OF THE ACADEMY OF [1881. 



Geological Position^ etc. — Found thus far only in the Upper 

 Silurian of Sweden. 



1878. Briarocrinas inflatus Angelin. Iconogr. Grin. Suec, p. 1, PI. 10, fig. 23. 



Upper Silur. (rothland, Sweden. 

 (?] 1878. Briarocr. angustus Angelin. Iconogr. Grin. Suec., p. 1, PI. 10, fig. 22. 



Upper Silur. Gothland, Swei'en. 



2. STELIDIOCRINTJS Angelin. 

 (Amend. Wachsmuth and Springer.) 



1878. Angelin, Iconogr. Crin. Suec, p. 21. 



1879. Zittel. Handb. der Palajont. , i, p. 345. 



Syn. Harmocrinus Angelin. Iconogr. Crin. Suec, p. 23. 



We are obliged to include Angelin's genus Harmocrinus in 

 Stelidiocrinus. A few additional interradial or interaxillary 

 plates do not alone warrant a generic or even subgeneric separa- 

 tion. According to Angelin and Zittel, StelidiocrinuH and 

 Harmocrinus, with Hall's Schizocrinus, form a distinct famil}'. 



The genus now under consideration is in more than one respect 

 an interesting form with reference to the Palaeontologic history of 

 the Crinoids. It is the only genus of the Actinocrinidae which 

 has five basal plates, none of them being anchylosed, and as this 

 is one of their earliest representatives, there can be little doubt 

 that the basals in this family, whether composed of a single piece 

 or of three or four, were derived originally from five. The rela- 

 tions also between this genus and Divierocrinus of the Rhodo- 

 crinidse are so close, that it may be asked whether the presence of 

 underbasals, which form the only distinction, should be considered 

 of more than generic importance. It shows, at all events, the 

 very close relations that exist between the two sub-families. There 

 is also to be seen within the limits of this genus, a modification 

 of the arms from interlocking single joints to a double series of 

 plates. 



Generic Diagnosis. — Body small. Calyx subturbinate or sub- 

 ovate, without surface ornamentation ; radial plates prominently 

 elevated above the interradial areas, but not producing sharp 

 carinae. 



Basals five, equal, quadrangular, upper angles acute. Primary 

 radials 3X5; the first large, wider than high, lunate, hexagonal ; 

 the second quadrangular, shorter and much narrower ; the third 

 pentagonal, almost as wide but not as high as the first. Second- 



