ECHINOMETRA. 371 



Brunli differ from the other members of the genus, in that ocular V is insert 

 in the great majority of specimens, whereas in all of the others the oculars 

 are usually all exsert. It is interesting to note that in Van Brunli, which is 

 most progressive as regards number of elements in an ambulacral plate, we find 

 the most progressive abactinal system, oculars V and I being insert in nearly 

 three quarters of the specimens. The largest Echinometras seen are from 

 Bermuda and the Abrolhos Reefs, Brazil. They measure from 85-95 mm. in 

 length and are about 75-85 mm. wide and 42-48 mm. high. Great diversity 

 is shown in the genus in the relative length, breadth, and height of the test. 

 The breadth ranges from .75 to .96 of the length; when it is as much as .95, 

 small specimens of course appear to be circular in outline. The height ranges 

 from .40 to .63 of the length ; as a rule low specimens are wide and high speci- 

 mens are narrow. 



In distinguishing the seven species herein recognized, the number of pore- 

 pairs in an arc is considered of first importance, for while there is more or less 

 variation from the normal number, yet in the mid-zone and above, the variation 

 is slight, until one approaches the ocular; of course in young specimens, the 

 largest number of pores will be above the-mid-zone. The form of the test, the 

 structure of the auricles and the character of the primary spines prove to be 

 more or less useful points in most of the species. The pedicellarise are of little 

 use, though the tridentate have a characteristic form in at least one species. 

 In some cases, color may be of use for distinguishing a given species but it is 

 very unreliable and in Mathcei at least is almost useless. The size and tubercu- 

 lation of the abactinal system and even the form of the abactinal secondary 

 spines are useful characters in recognizing some species. 



The following table shows how the seven species may be distinguished: 



Pore-pairs, at or above ambitus, 4 or 5 in each arc, and not rarely 6. 

 Pore-pairs in arcs of 4, not rarely 5. 



Color very rarely black; primary spines variable but usually pointed and 



their thickness generally much less than ten per cent of their length. 



Height of test usually .55-.6S of length; abactinal system .15-.25 of 



test-length; usually 3 or more secondary tubercles on each genital 



plate; color of primary spines very variable, often dark purplish or 



reddish, frequently tipped with yellow or red . . Mathcei. 



Height of test less than half the length; abactinal system .20-.30 of 

 test-length ; seldom more than one secondary tubercle on each genital 

 pla{e; primaries usually light fawn-color or greenish, but sometimes 



dark with light tips picla. 



Color usually black, rarely dull purplish gray or even dull red; primary 

 spines short, stout, and usually blunt, their thickness .12-.22 of their own 



