1896.) GENUS OF FOSSIL ECHINODERMS. 1001 
II. Description of Lysechinus. 
LYsECHINUS *, noy. gen. 
Diaenosis.—Plesiocidaroida with the ambulacra limited to 
grooves on the oral half of the test. 
Descrivtion.—Zest small and slightly elliptic; margins tumid ; 
oral and apical surfaces flattened. 
Apical system very large, and forming most of 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. 
Periproct large ; an irregular pentagonal ellipse. 
Ambulacra.—These occur in five (?) somewhat spoon-shaped 
depressions around the mouth. There are four or five small 
single pores on each side of each ambulacrum. 
Interambulacra 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 mn. 
Diameters oceetackesdem tes tes dimias 
Diameter of periproct .. 13 ,, 
a 97, PELISLOMIE -.5 samt 
Disrrreution.—St. Cassian Schichten. Trias: St. Cassian, Tyrol. 
Typn Spucrus *.—Lysechinus incongruens, n. sp. Brit. Mus., 
E 3935, 
Ill. 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 
1 From dvars, dissolution or disconnection. In Prof. Bell’s ‘Catalogue of 
British Echinoderms,’ 1892, pp. 14, 24, the term lissactinic is used as a synonym 
of azygopodous. This is obviously a printer's error, A\vots having been mistaken 
for \tcoos, smooth. ‘The slip is here corrected at Prof, Bell’s request ; the word 
should be “ lysactinic.” 
2 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. 
