﻿GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE, 107 



hmiiie which is characteristic in Encope of the posterior interambiila- 

 crum 5. This is most interesting and is discussed later at length. 



The type-specimen measures 86 mm. in length, 89 mm. in width, 

 and 8 mm. in height. The highest point is distinctly anterior to the 

 middle of the test. The specimen represented by a mould of the 

 ventral side is somewhat larger than the type. It measures about 

 93 mm. in length by about 96 mm. in width. 



In the type, the ambulacral petals are broad, about equal in length 

 in the several areas, the posterior pair extending back to a line with 

 the anterior limit of the lunule in interambulacrum 5. Ventrally, the 

 ambulacral fu.rrows are deep, slightly curved outward from the 

 median line of each ambulacrum, forking near the border of the test, 

 each furrow giving off a forked branch at nearly a right angle to the 

 main furrow. The apical disk is central, but details are obscured 

 owing to local imperfections in both specimens showing the dorsal 

 side. Interambulacral areas are narrow in the petaloid areas, wide 

 near the margin of the test. The whole dorsal surface of the test is 

 covered with small tubercles; on the ventral side of the test the 

 tubercles are somewhat larger, but they are reduced in size or want- 

 ing along tlie lines of the ambulacral furrows. The mouth is small 

 and central in position. The periproct is small, oval in outline, and 

 situated at nearly one-third the distance from the mouth to posterior 

 border of the test. 



The lunule of interambulacrum 5 is the remarkable and most in- 

 teresting feature of this species. Ventrally, it consists of an im- 

 pressed area 15 mm. long by 2 mm. wide, extending to and being 

 confluent with the opening of the periproct. Dorsally, the lunule 

 also consists of an impressed area lying above the middle of the ven- 

 tral lunular depression and measuring 10 mm. in length by 2 mm. in 

 width. This is the only species in the genus recorded in which the 

 lunule fails to make an opening through the test. Structually, it 

 is most interesting, as it closely resembles the condition in a young 

 specimen of Mellita sexiesj^erforata (Leske) from the west coast of 

 Florida, 30 fathoms. No. 2900, Museum of Comparative Zoology. 

 This young Mellita, which measures 9 mm. in length, has no notches 

 or lunules as yet developed in the ambulacral areas, but in interam- 

 bulacrum 5, as viewed ventrally, there is a distinct impressed area 

 marking the initial beginnings of a lunule as in our specimen of adult 

 Encope annectans. It should be stated that this specimen of Mellita 

 is probably exceptional in holding this youthful character so late, as 

 in a small series of younger specimens of M. sexiesperforata measur- 

 ing from 4 to T mm. in length, all have a perforate lunule in interam- 

 bulacrum 5. This latter set is from Salt Key, Bahamas, No. 2439, 

 Museum of Comparative Zoology. As pointed out by Mr. Agassiz 

 (Eevision of the Echini, pp. 320-324) in Mellita sexiesperforata^ the 

 8370''— 18— BnlL 103 S 



