OCR Text |
Show 1884.] PROF. F. J. 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 Echinanthus ; 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 l, 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 orthostichous passed to thepetalostichous 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 Echinanthus 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 aud 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 Olypeasters with the petals still open and the actinal grooves developed. |