GEOLOGY AND PALEONTOLOGY OP THE CANAL ZONE. 159 



Measurements. — Length of palm between articulations, 19 mm. ; 

 height (approx.), 10.2 mm. 



Represented by the left palm only, which has the customary Calap- 

 poid form, and a portion of the immovable finger ; the edges are not 

 well shown ; two teeth may be seen near the distal end of the upper 

 margin. The only details of the outer surface that can be made out 

 are a few large tubercles, more or less compressed as in Recent species 

 of Mursia; these tubercles number about 15; there is a row of 4 

 a little above, and subparallel to, the lower margin ; from these 4 

 tubercles irregular rows extend obliquely upward, trending toward 

 the fingers ; including those of the horizontal row, those of the distal 

 oblique row are 4, of the second row 5, of the third row 3, of the 

 proximal row 3; these rows are not strictly parallel nor their tuber- 

 cles regularly spaced. The lower proximal tubercle is the largest and 

 most compressed. 



There is an indication of the distal spine of the arm- joint, which 

 may be seen in the figure. 



Resembles Mursia armata de Haan, 1 but in that species the prin- 

 cipal tubercles of the hand are 9, arranged in 3 parallel and fairly 

 regular rows. 



MURSIA OBSCURA, new species. 



Plate 61. fig. IS. 



Type-locality. — Near Panama Canal Station "1910," north of 

 Pedro Miguel locks, Panama Canal Zone. From dark clay, lower 

 part of Culebra formation. Oligocene series. D. F. MacDonald 

 and T. W. Vaughan, collectors. 1911. Station 6010. Cat. No. 

 324225, U.S.N.M. 



Measurements of fragmentary specimen, 8.2 mm. long, 9 mm. wide. 



Holotype. — The central part of the carapace, devoid of its margin, 

 except perhaps the middle of the posterior margin. This fragment 

 is embedded wrong side up in a piece of rock; only the thin outer 

 crust of the specimen remains and its under surface alone is visible. 

 It has been referred to this genus because the cavities or pits, which 

 represent tubercles on the dorsal surface of the shell, are arranged 

 much as in Mursia. There are 5 longitudinal rows of these pits : The 

 median row consists of 3 large pits., one cardiac, one genital, one gas- 

 tric, preceded by 2 small pits side by side; the two lateral rows 

 (on each side) are very little oblique to the median line, but sub- 

 parallel to each other ; the inner of these rows consists of 4 pits, the 

 penultimate one being in a transverse line with the last pit of the 

 median row ; the last pit of the inner lateral row is round and deep 



1 Fauna Japonica, 1839, p. 73, pi. 19, fig. 2. 



