438 



PROF. F. J. BELL ON THE TEMNOPLEURID^. [Juiie 1, 



The diminution in the proportional size of the abactinal or actinal 

 areas is very fairly shown by this Table. The auricular foramen is 

 sometimes almost a complete square ; the auricles vary a little in 

 height, but the connecting ridges are always low. The spines may 

 be all white, or they may be of a light brick-red. 



4. Amblypneustes pallidus. 



Just as it is possible to distinguish a number of forms which, by 

 their exquisite pattern, are seen to be specimens of A. formosus, so, 

 too, it is possible to separate off a series of forms in which the 

 pattern on the test is only visible on very close examination ; these 

 can at any rate be ranged under the head of A. pallidus. When the 

 succeeding Table of measurements is compared with that of A. 

 formosus, it will uot be hard to formulate certain differences between 

 them : the fifth specimen is interesting as presenting the oviform 

 arrangement in having the height greater than the diameter ; and 

 here, as in A. formosus, we find an example of how greatly the 

 species of this genus may vary in form. We find, moreover, that iu 

 A. pallidus (saving always specimen v.) the abactinal area increases 

 in size with an increase in diameter, whereas in A. formosus it 

 diminishes very markedly ; so, again (again excepting v.), we find 

 the actinostome to be not much larger or much smaller proportionately 

 in specimens of different sizes, while iu A. formosus the actinostome 

 diminishes very much in size at a comparatively early stage, and 

 then varies within considerable limits. These, however, though real 

 characters, are not easily grasped, and it is difficult to say what 

 points of distinction can be at once appealed to as readily accessible 

 to the zoologist. 



Prof. Alex. Agassiz states that the only points of difference which 

 he can find between them are : — 



( 1 ) The slight development in A. pallidus of the coloration and 

 pattern of sculpture so distinctive q( A. formosus. 



(2) The presence of secondaries and small miliaries in the narrow 

 poriferous zone of A. pallidus. 



(3) The less numerous median sutural pores of the same form. 



(4) Tlie greater uniformity [in size] and more irregular arrange- 

 ment of the tubercles of A. pallidus^. 



^ I base this view on the supposition that the woi'd " separate," in line 9 of 

 p. 482, is a lapsus j^luma for "imite." 



