FOSSIL ECHINOIDS OF JAPAN. 19 



Ambulacra diverse ; the anterior one in a broad groove, pores 

 not obliterated, fewer in number than those of other petals, round 

 and small ; interporiferous area thickly provided with secondary 

 tubercles. The lateral ambulacra sunken and slender ; the anterior 

 making an angle of 35° with the odd ambulacrum, straight and 

 reaching almost to the ambitus ; the posterior shortest and also 

 straight. Poriferous zone wide, and the interporiferous area shallow, 

 occupying nearly one third of the width of the petals. It is to 

 be noticed that all the petals are nearly straight and retain the 

 same width throughout their whole length, except near the vertex. 

 The number of pores in the anterior lateral petal 39, and in the 

 posterior one 28 in the largest specimen ; interporiferous area of 

 the paired ambulacra very narrow, leaving no space for tubercles. 

 Peripetalous fasciole narrow, angular with a deep reentering 

 angle in the anterior and posterior lateral ambulacra; undulating 

 at the anterior ambulacrum and deeply entering outside, but almost 

 nearly straight in the posterior interambulacrum. The lateral 

 fasciole sloping toward the ambitus, abruptly curved near the 

 posterior edge, and passing under the anus. 



Actinal surface flat ; actinostome situated at about one fourth 

 the distance from the anterior edge. Anus elliptical, visible only 

 in a side view. The tubercles of the abactinal surface very small and 

 uniform in size, those of the actinal surface large and also uniform. 

 The living species of Linthia are now found in Australia, 

 Tasmania, the Arafura Sea and the West Indies ; fossils have been 

 discovered in the Cretaceous of Europe, Africa, N. America, and 

 in the Tertiary of Europe, Africa, W. Sind and the West Indies. 

 The general outline, the shallow anterior groove, and the long antero- 

 lateral petals, are characters which justify us in placing this species 

 under Llitthla rather than under Schizaster. 



