FIBULARIA OVULUM. 507 



largo, distant ; intermediate space packed by minute miliaries on the lower 

 surface ; the tubercles become more distant towards the actinostome, which is 

 surrounded by five smooth bands, formed of very minute tubercles, much as 

 in the bourrelets and their prolongation in the Cassiduloids. 



In smaller specimens not measuring more than 8 mm ' in longitudinal diam- 

 eter (6 mm transverse), the proportionally shorter open petals and. more 

 pointed posterior edge are the only differences noticed. Auricles nearly as 

 prominent as in Eehinocyamus ; jaws compact, high, like the jaws of Echino- 

 cyamus. There are no additional pillars between the two floors, developed 

 with age, as the presence in the young of anal posterior ridges on the two sides 

 of the anal opening connecting the upper and lower floors would lead us to 

 suppose. They are the homologue of the radiating partitions of Eehino- 

 cyamus, but neither do they extend to the mouth, nor are additional walls 

 formed, as in that genus. The smallest specimens examined did not measure 

 more than 2 mm -, longitudinal diameter ; they differed from older specimens by 

 their more regularly arched abactinal surface, and the small size of the anal 

 opening ; its position was identical with that of older stages ; the number of 

 disconnected pores (three and four pairs) forming the rudimentary petals is 

 small ; they only diverge a short distance from the apical system. 



This sj^ecies was originally placed in Eehinocyamus ; the internal differ- 

 ences are, however, sufficient to separate it from Eehinocyamus proper, viz. 

 the absence of the anterior and interior radiating partitions. Gray sep- 

 arated this species as an independent genus (Mortonia). I have removed it 

 from Eehinocyamus to Fibularia, with which, from the absence of lateral 

 radiating partitions, it seems most closely allied, but I am by no means satis- 

 fied that the genus Eehinocyamus and Fibularia are properly distinguished, 

 and that future study among these small Echini, with better material, will 

 not modify the views of their affinities here suggested. 



Sandwich Islands ; Japan ; Australia. 



Fibularia ovulum 



Echinus minutus Pali... 1774, Spic. Zool , IX. PI. I.f. 3". 

 ! Fibularia ovulum Lamk., 1816, An. s. Vert., p. 17. 



PL XHP.f. is. 



This is the most common species of Fibularia in our collections, known and 

 quoted under a multitude of names, from the figures of Van Phelsum, yet 



