ENCOPE. 73 



material Mr. Agassiz has accumulated in the M. C. Z. collection from both sides 

 of tropical America, shows well the variability in form of both test and lunules 

 which characterizes some of the species. Nevertheless other species, particu- 

 larly grandis, show very little diversity and we ought to recognize six species, 

 since one of the forms, named perspectiva by Agassiz in 1841, and considered 

 in the Revision as a form of micropora, seems quite distinct. The solidity of 

 the test, the position of its apex, the position of the lunules, and the length of 

 the petals furnish the best characters for separating the species. The size of 

 the lunules may also be of use but in some cases, especially in emarginata, it is 

 most unreliable. 



The spines show no noteworthy peculiarities. The pedicellariae are all 

 bivalved and small. It is difficult to draw any line between bidentate and bi- 

 phyllous forms, for the two extremes intergrade so completely. The form of the 

 blade differs somewhat in the different species, as will be noted below, but it is 

 doubtful if these differences are perfectly constant. The disks of the tube-feet 

 have rods in them much as in Echinarachnius. 



Key to the Species of Encope. 



Test moderately heavy with margins rarely exceeding 3 mm. in thickness, and usually 

 much less. 

 Test as high anterior to abactinal system as it is posteriorly and often distinctly 

 higher. 

 Test elevated equally both anterior and posterior to abactinal system; inter- 



ambulacral lunule large, variable in form, its length, .16-.35 test-length . emarginata. 

 Test distinctly highest anteriorly; interambulacral lunule variable in form, 

 small, its length only .10-. 17 test-length. 

 Anterior end of interambulacral lunule nearer distal end of posterior petals 



than to center of abactinal system micro para. 



Anterior end of interambulacral lunule nearer to center of abactinal system 



than to distal end of posterior petals perspectiva. 



Test highest back of abactinal system, at anterior end of interambulacral lunule. 



Ambulacral marginal slits rarely, if ever, closed to form lunules, often reduced in 

 the anterior ambulacra to mere notches or even entirely wanting there; peta- 

 loid area large; posterior petals about .33 test-length and unpaired petal nearly 



or quite as long michclitii. 



Ambulacra with completely closed, rounded lunules; petaloid area moderate, 



none of the petals, much exceeding .25 test-length califamica. 



Test very heavy, about as wide ai long; margin about 5 mm. thick; interambulacral 

 lunules big and round; marginal notches wide, not very dee]), rarely, if ever, closed to 

 form lunules; posterior petals .35-. 40 test-length ; unpaired petal about .66 posterior . grandis. 



