1884.] PROF. F. 3. BELL ON ECHINANTHUS TUMIDUS. 43 



Echinolampas depressa. Yet, again, the pores may become completely 

 confined to the abactinal side of the test, as in Clypeaster or Echi- 

 nanthus ; but, when this happens, there is a marked tendency, in all 

 known genera, for the distal pores to approach, and the median 

 pores to separate from their fellows of the corresponding pair ; to 

 produce, in fact, a petal-like arrangement of the poriferous zones. It 

 is clear that, in the history of development, there must be a time when 

 the pores are open \ and more or less regularly arranged in parallel 

 rows, and it is no less clear that at no time would there be, of necessity, 

 any tendency to a spreading or widening out of the poriferous zones, 

 in the mode here compared to that of a lyre ; nor is this more than 

 indicated in the form now before us ; but the tendency is distinct 

 enough to remove the species from the direct line of ancestry through 

 which the ortkostichous passed to the petalostichous Echinid. 



It is necessary therefore to distinguish the generic position of the 

 form, and I propose to call it Anomalanthus, and to define it in the 

 following terms : — 



A petalostichous Echinid in which the ambulacral pores are 

 arranged in rows which are not closed or quite parallel, but which 

 tend to spread out after a lyre-shaped fashion at their distal end. 

 The actinal surface is free of pores and has the ambulacral sutures 

 of Echinanthus, which are not, however, converted into conspicuous 

 grooves. Mouth deeply sunken. Anus a little elongated transversely, 

 placed exactly at the ambitus. Five genital pores, not all of the 

 same size ; one ocular pore very large. Primary tubercles perforate, 

 regularly distributed over the whole test. Its nearest allies are Echi- 

 nanthus and Clypeaster. 



The fact that the outer rows of pores are ordinarily larger than 

 those of the inner allies this genus to Clypeaster and Echinanthus, 

 while the great irregularity in the size of the pores shows that the 

 whole system is in a fluid or plastic condition. The fact that, as 

 yet, only one specimen is known, indicates that the form is rare ; 

 indeed in all possibility it is dying out. Like other members of the 

 terrestrial and marine fauna of Australia, we have indications of long 

 continued existence as a distinct species, coupled with an incapacity 

 to live in large numbers in the presence of organisms more plastic 

 and more easily adaptable and adapted to the conditions of their 

 present environment. 



The enthusiasm of the naturalists of Australia will, no doubt, 

 continue to bring to light forms such as this, which, by indicating 

 some of the conditions and causes of failure, will throw an oblique 

 light on the mechanical conditions of success, and enable us to add 

 to laborious and detailed descriptions of specimens some reasonable 

 suggestions as to their relationships and history ; to convert, in fine, 

 a science of observation into a philosophical inquiry into the causes 

 of things. 



1 In the 'Eevision of the Echini' (pi. xiii. figs. 16-18) there are figures of 

 young Clypeasters with the petals still open and the actinal grooves developed. 



