DIALITHOCIDARIS. 75 



DiALITHOCIDARIS. 



A. Agassiz, 1898. Bull. M. C. Z., XXXII, p. 75. 



Type-species, Dialithocidaris gemmifera A. Agassiz, 1898. Bull. M. C. Z., XXXII, p. 75. 



This monotypic genus is still known only from the single specimen 

 collected by the "Albatross" in 1891, off Mariato Point, Panama, in 1793 

 fathoms. 



Dialithocidaris gemmifera A. Ag. 



Dialithocidaria gemmifera A. Agassiz, 1898. Bull, M. C. Z., XXXII, p. 75. 

 1904, Mem. M. C. Z., XXXI, p. 56 ; Pis. XV, figs. 3-5 ; XXIII. 



Plate 46, figs. 9-16. 



Although not taken by the " Albatross " since 1891, we include this 

 species in order to describe and figure the pedicellariae. 



The tridentate pedicellaria3 (fig. 9) are common, as many as 4-6 occurring 

 on each of the coronal plates. They are very large in proportion to the 

 diameter of the test. The valves (figs. 10 and 11) are strongly compressed, 

 especially just above the apophysis, and are coarsely serrate. They measure 

 from 2 to 2.5 mm. in length, while the stalks are twice as long. The upper 

 end of the stalk (fig. 12) is flattened and expanded. 



The ophicephalous jDcdicellariae (fig. 13) are abundant, particularly near 

 and upon the abactinal system. The valves (figs. H, 15) are stout, almost 

 flattened at the tip and strongly constricted near the middle. They are 

 only .30-.45 mm. long, while the stalks may be 6-8 times that length. 



The triphyllous pedicellariae are much less common than either of the 

 other kinds. The valves (fig. 16) are somewhat flattened and rounded at 

 the end ; they measure .35-.40 mm. in length, and the stalks are 6-8 times 

 as long. 



The calcareous deposits in the pedicels seem to be very scarce. They are 

 simple, perforated plates, so narrow as to be hardly more than flat rods with 

 irregular margins, and little or not at all curved. 



The sphaeridia are situated one in each ambulacrum, on the peristome, 

 and are not in a marked depression, though the test behind each is slightly 

 hollowed. 



