N0.221S. FOSSIL ECHINI OF PANAMA CANAL ZONE— JACKSON. 497 



wide in areas II and V, indicating that this is the character in the 

 two posterior ambulacra I and V and also in the paired anterior am- 

 bulacra II and IV. This evidence is supported by several of the frag- 

 ments which show shallow lobes like the type, but it can not bo 

 definitely stated which areas they represent. The notch of the ante- 

 rior odd ambulacrum III is not known, but it was probably shallower 

 than the others, as is characteristic of species of the genus. The most 

 striking feature of this species is the lunule in intorambulacrum 5, 

 which is enormous. It is situated about midway between the apical 

 disk and posterior limits of the test, is roughly triangular in shape, 

 the apex of the triangle pointing anteriorly. It measures at the 

 surface of the opening 27 mm. in length and 27 mm. in width at the 

 widest part posteriorly. The walls of the lunule slope outward from 

 the center, as seen looking from above, as is well shown in two of the 

 fragmentary specimens. From this sloping character of the walls, it 

 results that the width of the lunule would bo greater by about G to 



10 millimeters on the ventral side than it is on the dorsal. The height 

 of the wall of the lunule is 12 mm., which is doubtless the highest 

 point of the test. The lunule in this species is, relatively to the size 

 of the spocim.ens, the largest known in any species of the genus, 

 fossil or living. It is striking that this groat size of the lunule, a 

 progressive character, should be associated with small and shallow 

 ombulacral notches which, for the genus, is a relatively primitive 

 character. 



The ambulacral petals are beautifully distinct and well preserved 

 for part of their extent in the type and one other specimen. The 

 posterior pair, I and V, are long and narrow with a relatively wide 

 poriferous area and narrow m.edian interporifcrous area. The width 

 of the petal of ambulacrum V is 11 mm. and its length is 50 mm. It 

 extends posteriorly in a wide curve around the lunule of intorambu- 

 lacrum 5 and reaches a line coincident with the posterior end of the 

 lunule. It also extends to within 5.5 of the ambulacral notch of the 

 area in which it lies. Ambulacrum IV is much shorter than ambiJa- 

 ci-um V, measuring 30 mm. in length and 12 mm. in width at its 

 widest part. This ambulacrum extends to within 3.5 mm. of its 

 marginal notch. The features of the ambulacra V and IV as described 

 indicate the character of ambulacra I and II, which are only preserved 

 in part in the holotype, though one of the fragments has ambulacrum 



11 quite perfectly preserved. Ambulacrum III is represented only in 

 part (for a length of 25 mm.) by the left side of its petaloid area; it 

 probably had about the length and width of the petal of ambulacrum 

 IV, as in the allied species Encope macrophora Ravenel. Ambulacral 

 furrows on the ventral side are deep, strongly marked with some 

 forking near the periphery of the test. The interambulacra are very 

 wide, not narrowing markedly near the apical disk. Minute tubercles 



77403— Proc. N. M. vol. 5^—17 32 



