494 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 53. 



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. annedans resembles Encope micro- 

 pora Agassiz of the West Coast in the form of the test and the posi- 

 tion of the interambulacral lunule. 



Locality and geologic occurrence. — Gatun formation, upper Oli- 

 gocene or Miocene, Panama Canal Zone, Spillway at Gatun Dam 

 site, D. F. MacDonald, collector, U. S. National Museum station 

 No. 5846, three specimens. 



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

 U.S.N.M. 



ENCOPE PLATYTATA, new species. 



Plate 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- 

 nedans, this species, E. plaiytata, is thin, flattened, and if complete, 

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

 buiacral 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 ambuiacral notch of area III is very shallow and 

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

 are also roimdod 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 annedans. This lunule is only preserved for the anterior 

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

 central in position, the periproct is elongate oval, its anterior border 

 is 13 mm. posterior to the border of the mouth opening. Poste- 

 riorly the periproct is confluent with the infolded depression of the 

 interambulacral lunule. 



The ambuiacral petals are rather narrow in this specimen, measur- 

 ing 13 mm. in width. The odd anterior ambulacra! petal is longei 

 than the others, and measures 36 mm. in length, whereas the pos- 

 terior petals of the trivium measure 28 mm. in length. The petals 

 of the bivium, or I and V, are longer than the posterior pair of the 

 trivium, but as they are incomplete posteriori}^ a measurement can 

 not be given. On the ventral side, the ambuiacral furrows are 

 strongly marked and each gives off a few weakly impressed branches. 



