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Show 1000 DR. J. W. GREGORY ON A NEW [Dec. 15, 4. O n Lysechinus, a new Genus of Fossil Echinoderms from the Tyrolese Trias. By J. W . G R E G O R Y , D . S C , F.G.S., Assistant in the British M u s e u m (Nat. Hist.). [Received October 22, 1896.] (Plate LI.) Page I. Introduction 1000 II. Description of Lysechinus incongruens, gen. et sp. nov 1001 III. Affinities of Lysechinus and Classification of the Plesiocidaroida. 1001 IV. Affinities of the Plesiocidaroida 1003 I. Introduction. The genus Tlarechinus was founded by Neumayr1 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 Archseocidaridse, Cidaridae, and Diadematidae. H e included it temporarily in tbe first-named family, but thought it would probably be necessary to institute for it a new order, intermediate between the Palseechinoidea 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. H e thought that he could recognize certain sutures by the use of glycerine, but it was reserved for Loven2 to prove that each interambulacrum consists of four plates, three vertical plates resting on a single oral plate. This discovery showed that Tlarechinus was even more abnormal than Neumayr thought. Duncan3, in 1890, according^ 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 tbe Klipstein Collection in the British Museum, which I at first regarded as a new species of Tlarechinus, 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. 1 M. Neumayr, " Morphologiscbe Studien iiber fossile Echinodermen," Sitz. k. Akad. Wiss. Wien, Bd. lxxxiv. Abt, 1. 1881, pp. 169-176, pl. ii. fig. 4. 2 S. Loven, " O n Pourtalesia," Handl. K Svens. Vet.-Akad. Bd. xix. 1883, no. 7, pp. 12, 65, pl. xiii. 3 P. M.Duncan. " A Revision of the Genera and Great Groups of- the Echinoidea," Journ. Linn. Soc, Zool. vol. xxiii. 1890, p. 19. |