J.896.] GBNUS OP FOaSIL EOHINODBEMS. lOOl 



II. Description of Lysechiuus. 

 Lyseohinus \ nov. gen. 



Diagnosis. — Plesiocidaroida with the ambulacra limited to 

 grooves on the oral half of the test. 



Desceiption. — Test small and slightly elliptic ; margins tumid ; 

 oral and apical surfaces flattened. 



Apical system very large, and forming most o£ the test. The 

 basal ring consists of five plates, forming a closed ring. One 

 (? more) of these is perforated by a pore. Their form is apparently 

 heptagonal. 



Ocular plates very large ; they are hexagonal ; five of the sides 

 are straight, but the sixth is broken by a notch for the end of the 

 ambulacrum. 



Penproct large ; an irregular pentagonal ellipse. 

 . Ambulacra. — These occur in five (?) somevchat spoon-shaped 

 depressions around the mouth. There are four or five small 

 single pores on each side of each ambulacrum. 



hiterambulaera large. Apparently each consists of nine plates ; 

 there is a large single peristomal plate succeeded by two plates, 

 above which are two series each of three plates. 



The ornamentation consists of granules or small tubercles 

 irregularly arranged. The spines are short, with a stout proximal 

 knob. 



Peristome very large, occupying nearly the whole of the lower 

 surface of the test. 



Dimensions. — Height 4 mm. 



Diameter 7 „ 



Diameter of periproct . . 1^ „ 



„ „ peristome . . 3g „ 



DiSTEiBUTioN. — St. CassianSchichten. Trias: St. Cassian, Tyrol. 

 TrPE Species °. — Lysechinus incongrueiis, n. sp. Brit. Mus., 

 E 3935. 



III. Affinities of Lysechinus and Classification of the 

 Plesiocidaroida. 



The interpretation of the specimen on which this genus is 

 founded is unquestionably difficult, owing to its small size, to the 



' From XuVis, dissolution or disconnection. In Prof. Bell's 'Catalogue of 

 British Eohinoderms,' 1892, pp. 14, 24, tlieterm lissactinicisused nsasjuonym 

 of azjgopodous. This is obviously a printer's error, XvatK baving been mistaken 

 lor Xitrffd?, smooth. The slip is here corrected at Prol'. Bell's request ; the word 

 sliould be " lysactinic." 



^ There being only the one species it is impossible to say which of the 

 characters are specific and which generic. No specific diagnosis is therefore 

 possible. 



