666 Springer — Mysticocrinus. 



Aet. XXXV. — On Mysticocrinus, a new genus of Silurian 

 Crinoidea; by Feank Speingee. With. Plate II. 



Among recent collections from the Laurel formation 

 of Magaran age in southern Indiana, there has appeared 

 a small crinoid of wholly novel type, — one of those aber- 

 rant forms which occur from time to time to perplex the 

 systematist and delight the morphologist. It is an Inad- 

 unate, superficially resembling the Larvif ormia, but 

 departing from their general facies in having a dicyclic 

 base. It would seem to be intermediate between the 

 Larviformia and the Fistulata, but without any close 

 connection in either group ; in the composition of the cup 

 it resembles the Dendrocrinidae, although wholly unlike 

 them in the primitive character of the arms. In the lat- 

 ter respect it is somewhat similar to Haplocrinus, which 

 has extremely short, unbranched arms, as is shown by a 

 specimen in my possession not yet illustrated. In calling 

 this peculiar form the "mysterious crinoid' ' we have an 

 appropriate designation which accords well with its 

 strange characters. 



MYSTICOCRINUS nov. gen. 

 ( MvotZkos — mysterious ; KpiW — lily ) 



Calyx rigid, globose, contracting at the arm bases, with 

 no indication of loose suture or flexibility in cup or teg- 

 men (thus excluding Flexibilia). Tegmen narrow, prob- 

 ably covered by a pyramid of orals as in Pisocrinus 

 and Symbathocrinus. Lower brachials do not take part 

 in the formation of the calyx wall, i. e., no interbrachials 

 (excluding Camerata). 



Base dicyclic ; IBB 3, the small plate in right posterior 

 position. Radianal in primitive position below r.post.- 

 ray. Anal plate" 1, large, angular distally, projecting 

 above level of RR. RR 5: the right posterior one (and 

 no other) compound; arm facets curved and excavated, 

 not filling distal face of radials, some of them bounded by 

 processes projecting between the arm bases. Arms uni- 

 serial, short, composed of only a few ossicles. Anal 

 opening and tegmen unknown. 



Mysticocrinus wilsoni n. sp. 



Calyx very small — the size of Pisocrinus; flattened 

 below, strongly constricted at the arm bases. Plates 

 tumid, stem circular. 



