118 FOSSIL CRINOIDS. 



pointed out by Wachsmuth and Springer in 1881, who discovered the infra- 

 basals, not observed by PhiUips or other authors before. This made them 

 congeneric with Hall's later Thysanocrinus, which we then ranked as a synonym 

 under Phillips's genus (Rev. Pal., II, 198); an arrangement which we afterwards, 

 without good reason, reversed (N. A. Crin. Cam., 190), taking Hall's name, 

 Thysanocrinus, for the genus and family. This procedure has been justly criti- 

 cised, and must be abandoned. Therefore I use the names at the head of this 

 section instead of Thysanocrinidae and Thysanocrinus, as adopted in the North 

 American Crinoidea Camerata, and for the same generic type, viz : a Camerate, 

 dicyclic Crinoid, with radials in contact except at the anal side; several ranges 

 of interbrachial plates; biserial arms; and anus without a tube. Thysano- 

 crinus and Glyptaster clearly go as synonyms. Angelin's Eucrinus, which 

 included several species substantially like D. decadaciylus, was at first sought 

 to be upheld by restricting Dimerocrinus to species with only ten simple arms; 

 but the addition of another order of brachials, giving twenty arms simple like 

 the others, seemed such a very slight modification of the same plan of structure, 

 that this distinction was afterwards abandoned, and all the species thrown 

 together under Dimerocrinus except the two figured by Angelin as E. venustus 

 and E. minor (Icon. Crin. Suec, PI. XV, figs. 5, 7, 16). In these there is a 

 wholly different arm structure, with frequent branching at long intervals, and 

 the arms from the IIBr up, below the axillaries as well as above, biserial, as in 

 Megistocrinus, Abacocrinus, etc. These, however, appeared from the figures 

 to have the radials separated all around as in the Rhodocrinidae, and for them 

 we proposed the genus Anthemocrinus. 



What is of especial interest now, however, is that we have the first evidence 

 of persistence of this family type into the Middle Devonian. But for the non- 

 characteristic and somewhat obscure Lower Devonian form described by Jaekel 

 as Orthocrinus, the known species of this family have been restricted to the 

 Silurian and earlier. Schultze's " Rhodocrinus" quinquelobus, which he classed 

 with Thysanocrinus, and which we placed under Eucrinus (Rev. Pal., II, 197), 

 is monocyclic — a Batocrinoid, as will be shown later. A very distinct specimen 

 from the Hamilton beds near Louisville, with a calyx which cannot be excluded 

 from the family diagnosis, compels us to extend its range accordingly. 



