004 LINTHIA, 



LINTHIA. 



Desoria (Gray), 1851, Ann. Mag, X. II. (non Agass., 1841). 

 Linthia Mtn. 1S03. in Des. Act. Sue Helv. 



This genus unites structural features common to several genera. It has, 

 like Brissus, a shallow anterior groove, though quite broad, and lateral 

 anterior petals at right angles to the odd ambulacrum ; narrow, long, and 

 sunken lateral ambulacra. Peripetalous fasciole angular, re-entering in the 

 lateral interambulacra. Lateral fasciole extending under the anal system. 

 The general course of the fascioles and the principal features of the actinal 

 side are those of Agassizia. The general outline of the test and the structure 

 of the lateral ambulacra and the course of the peripetalous fasciole is that of 

 Brissus. 



I have associated Desoria with Linthia. It was fust distinguished by Gray 

 as Desoria, hut. as this name was preoccupied. 1 have retained its svnonvnic. 

 Linthia; it is. however, impossible in the present state of our knowledge 



of allied reeeiit Spatangoids to give any satisfactory reasons for associating 

 the only recent species with Linthia rather than with Periaster, nor do 1 feel 

 convinced that the generic characters assigned to Prenaster and Pericosmus 

 are sufficient to distinguish them accurately from fossil species alone ; for 

 they can be referred, to judge from the data obtained by the study ofrecenl 

 species, to either of the genera mentioned above. The greater or less dis- 

 tance of the peripetalous fasciole from the petals is not of great importance, 

 to judge from its variation in the young, as its proximity or distance appeals 

 to depend greatly upon age. 



The genera Periaster. Prenaster, Linthia (Desoria), Agassizia, and Schi- 

 zaster all agree in having a peripetalous fasciole and a lateral fasciole 

 branching from this, forming the subanal fasciole; the fact that in Linthia 

 the peripetalous fasciole follows the course of the ambulacra! petals is not 

 sufficient to separate it as a genus from Periaster. as was already suggested 

 by Desor, in his Synopsis. I would therefore propose to maintain the genus 

 Linthia. with Periaster as a subgenus, in which the peripetalous and lateral 

 fasciole are continuous, the peripetalous fasciole not surrounding the petals. 



