Verrill, JSFotes on Radiata. 587 



edge, but rises from the center to tlie posterior foramen, from which 

 it descends rapidly to the edge. The posterior interambulucrum is, 

 therefore, swollen and the test is most elevated near its foramen. 

 Ambulacral rosette with the petals long-oval, somewhat ohovate, 

 broadly rounded outwardly ; the anterior pair shortest and most 

 rounded ; the odd anterior one somewhat longer and narrower and a 

 little shorter than those of the posterior i)air, which ai'e of about the 

 same form and not curved. Posterior foramen variable in form and 

 size, usually rather small, regularly oval or rounded, sometimes long 

 oval, or even narrow and elongated, occasionally quite large and 

 broad oval, often obovate beneath, sometimes constricted in the mid- 

 dle. Ambidaeral foramina also quite variable in form and size, but 

 commonly small and rather regularly oval, often at a considerable dis- 

 tance from the margin. 



Two specimens, showing the extreme variations, give the following- 

 measurements : 



Leng-th of test,... 4-75 4-30 



Breadth, 465 4-30 



Center lo anterior edge, 245 2'15 



" " anterior foramen, TSO 1'65 



'• " lateral edge, 2-35 2-15 



" " " foramen, 1-60 1-50 



" . '■ posterior edge, 2-45 2'25 



'• " posterior-lateral foramen, .. ... TSS r70 



" " posterior foramen, ri5 I'lO 



Lengtii of •' " -67 -60 



Breadth of " '• -22 -26 



Length of anterior ambulacral petal, from center, ]/42 1 '32 



Breadth where widest, -65 -50 



Breadth of enclosed area, '30 'IS 



Length of anterior-latend petals, ... 1'28 I'lO 



Breadth, -67 '50 



Breadth of enclosed area,.. '28 20 



Length of posterior-lateral petals, rSS 1-35 



Breadth -(^B -53 



Breadth of enclosed area, -25 -16 



Of this species there are 74 specimens in the collection from La Paz, 

 and I have seen others from Cape St. Lucas. 



It varies considerably in outline and in the form of the openings, 

 especially the posterior one ; the ambulacral rosette varies somewhat 

 in the form of the petals, as shown by the above measurements ; the 

 ambulacral grooves beneath also vary in direction. But all the speci" 

 mens agree in having their greatest elevation behind the center, or 

 the posterior interambulacral region swollen. This peculiarity, which 



