1000 DR. J. W. GREGORY ON A NEW [Dec. 15, 
4. Ou Lysechinus, a new Genus of Fossil Echinoderms from 
the Tyrolese Trias. By J. W. Grucory, D.Sc., F.G.S., 
Assistant in the British Museum (Nat. Hist.). 
[Received October 22, 1896.] 
(Plate LI.) 
Page 
een GO CIGHION sn, dake cseaavetects coed Jcceaserenel susan take acre speaae saad 1000 
IL. Description of Lysechinus incongruens, gen. et 8p. NOV.......+..06 1001 
III, Affinities of Lysechinus and Classification of the Plesiocidaroida. 1001 
IV. Affinities of the Plesiocidaroida ...........sscjeceeesseceeseceneenccees 1003 
I. Introduction. 
The genus Tiarechinus was founded by Neumayr* in 1881 for 
a fossil from the St. Cassian Trias, which had been previously 
studied by Laube, whose name, however, had not been published. 
Neumayr described the fossil as an Echinoid having characters 
which allied it to the Archezocidaride, Cidaride, and Diadematide. 
He included it temporarily in the first-named family, but thought 
it would probably be necessary to institute for it a new order, 
intermediate between the Palzechinoidea and Euechinoidea. The 
main characters of the genus relied on by its founder were its 
large apical disc, short ambulacra, large mouth, and its having the 
granulation uniform, except for four small tubercles at the oral 
end of each interambulacrum. He thought that he could recognize 
certain sutures by the use of glycerine, but it was reserved for 
Loven*® to prove that each interambulacrum consists of four 
plates, three vertical plates resting on a single oral plate. This 
discovery showed that Yiarechinus was even more abnormal than 
Neumayr thought. Duncan’, in 1890, accordingly made it the 
type of a new order, the Plesiocidaroida, in which it has since 
been allowed to remain in solitary state. In the same year I found 
a specimen in the Klipstein Collection in the British Museum, 
which I at first regarded as a new species of Tiarechinus, an 
opinion which was shared by the late P. H. Carpenter, to whom 
I showed it; but a careful examination of the type specimen at 
Vienna, and of others there and in Berlin, showed that it was a 
distinct genus having the same type of structure. 
1M. Neumayr, * Morphologische Studien tiber fossile Echinodermen,” Sitz. 
k, Akad, Wiss. Wien, Bd. lxxxiv. Abt. 1, 1881, pp. 169-176, pl. ii. fig. 4. 
2S. Lovén, ‘‘ On Pourtalesia,” Handi, K. Svens. Vet. -Akad, Bd. xix. 1883, 
no. 4 pp. 12, 65, pl. xiii. 
P.M. Duncan. “A Revision of the Genera and Great Groups of the 
Bchinoidea.” Journ, Linn. Soc., Zool. vol. xxiii. 1890, p. 19, 
