108 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



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 invagina- 

 tion 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 

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

 forate. It makes an approach to the Recent Encope michelini 

 Agassiz of the Gulf of Mexico and E. grandis Agassiz of the Gulf of 

 California which are the only living species characterized by open 

 marginal notches* On the other hand, E. annectans resembles En- 

 cope micropora Agassiz of the West Coast in the form of the test 

 and the position of the interambulacral lunule. 



Locality and geologic occurrence. — Gatun formation, Miocene, 

 Panama Canal Zone, Spillway at Gatun Dam site, D. F. MacDonald, 

 collector, U. S. National Museum station No. 5846, three specimens. 



Type.— Cat. No. 324454, U.S.N.M. Paratype.— Cat. No. 324466, 

 U.S.N.M. 



ENCOPE PLATYTATA Jackson. 



Plate 51, figs. 1, 2. 



Encope platytaia Jackson, Proc. U. S. Nat. Mus., vol. 53, 1917, p. 494, text fig. 

 2 ; pi. 67, figs. 1, 2. 



There is only a single specimen representing this species, and 

 while it is imperfect, it yet has the essential parts preserved that are 

 necessary for a description. As in the last described species, E. an- 

 nectans, this species, E. platytata, is thin, flattened, and if complete, 

 apparently would be nearly circular in outline excepting for the am- 

 bulacral notches. If complete, the specimen would measure as esti- 

 mated about 100 mm. in length and 100 mm. in width. The greatest 

 height of the test is in the apical region, where it measures 10 mm. 

 As the ventral side of the test is somewhat concave instead of being 

 flat, the thickness of the test at the center, as measured by calipers, 

 is somewhat less than the height and measures only 8 mm. 



The anterior ambulacral notch of area III is very shallow and 

 rounded. The notches of the lateral anterior ambulacra II and IV 

 are also rounded but deeper than the notch of area III. Presumably 

 the notches of the posterior ambulacra I and V, if preserved, would 

 be similar but somewhat deeper, as this is the usual character in 

 associated species. The lunule in interambulacrum 5 is small, but 

 passes directly through the test instead of being imperforate as in 

 Encope annectans. This lunule is only preserved for the anterior 

 part of its extent as shown in the figures. The mouth is small and 



