No. 2218. FOSSIL ECniHil OF PANAMA CANAL ZONE—JACKSON. 493 



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 the hues of the ambulacral furrows. The mouth is small 

 and central in position. The periproct is small, oval in outhne, 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 ventral 

 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 tlirough the test. Structurally, it 

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

 specimen of Mellita sexiesperforata (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 MeUita 

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

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

 ing from 4 to 7 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 

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

 ambulacral and interambulacral lunules develop by resorption through 

 the test, whereas in the other species of Mellita, as far as known, the 

 ambulacral lunules are developed by the inclusion of marginal notches 

 and the interambulacral lunule alone is formed by invagination 

 through the test. 



Encope annectans is primitive like the other fossil species of Encope 

 in that the ambulacral notches are not inclosed to form lunules but 

 are still shallow and open. It is undoubtedly the most primitive of 

 tho genus in that the lunule in interambulacrum 5 is still imper- 

 forate. It makes an approach to the Recent Encope michelini Agassiz 



