1881.] NATURAL SCIENCES OF PHILADELPHIA. 303 



It makes but little difference whether the arms in Saccocrinus 

 speciosus (Hall's type) branch again after they become free, or 

 exclusively within the body as in the case of Periechocrinus 

 moniliformis, provided their mode of branching and their con- 

 struction otherwise is similar, and this is evidently here the case. 

 There are among the European species several in which the 

 arms branch in their free state, and we find among them all pos- 

 sible intermediate gradations, from two simple arms in the ray 

 to eight, and these either simple or branching. Angelin refers 

 species with only two and four arms, if remaining simple, to 

 Actinocrinus, but it seems to us, that a generic separation, based 

 upon the number of arms, cannot be upheld in a group in which 

 a branching of the arms is not onl}' admitted, but xevy charac- 

 teristic.^ 



Angelin 's Actinocr. medius and A. major have underbasals, and 

 are referred b}" us to the KhodocrinidjB. 



We place here with doubt Angelin's Periechocr. GoMandicus 

 and P. radiatus, which both differ in the secondary radials and in 

 the style of ornamentation from all other species, while they 

 agree on the same points and in their general aspect with Glypto- 

 crinus. ]S[one of the figured specimens show the anal side, and it 

 seems quite possible that the two species, like Glyptoerinus, had 

 no anal plates in line with the first radials. 



Periechocrinus grandiscutatus, P. multicostataSy P. undulatus, 

 P. annulatus and P. geometricus, Angelinas species,. were described 

 from fragmentary plates, and their identification is doubtful, the 

 latter even, if correctly figured, had underbasals. In that species 

 onl}^ the plates of the two proximal rings are known, those of the 

 second ring are angular above, instead of truncate, and hence the 

 succeeding ring must have been alternately arranged. 



According to our interpretation, Periechocrinus includes also 

 several species from the lower Subcarboniferous, which heretofore 

 have been variousl}^ referred to Actinocrinus, Megistocrinus, or 

 Pradocrinus, but only species with thin plates and elongate body, 

 leaving those with heavy plates, depressed body, and short radials 

 under Megistocrinus. 



We are aware that we include in this genus some species which 



^ In Actinocrinus the case is similar, some species having four, others 

 eight simple arms, and the last survivors of the genus have their arms 

 branching in the free state as in species of Periechocrinus. 



