NACOSPATANGUS GRACILIS. 149 



Nacospatangus. 1 



A. Agassiz, 1873. Bull. M. C. Z., 3, p. 189. 

 Type, Nacospatangus gracilis A. Agassiz, 1873. Loc. cit. 



Originally based on material taken by the Hassler, this genus has remained 

 little known. Mr. Agassiz (1904. Mem. M. C. Z., 31) has published notes 

 and figures supplementary to those in the Hassler report, but based on the 

 same material. I am now able to give an account of the pedicellariae and in 

 addition, to describe a second species. The study of all the available material 

 has not shown what the true relationships of the genus are. The character 

 of the ambulacra dorsally has led me to put it in the Palaeopneustidae but 

 this character is misleading and I am inclined to believe the nearest relatives 

 of Nacospatangus are in the Spatangidae, perhaps in the vicinity of Metalia 

 and Rhynobrissus. 



Key to the Species of Nacospatangus. 



Height of test .60 length; width over .80 length; test widest well back of apical system; 



globiferous pedicellariae with short teeth around mouth of valves gracilis. 



Height of test about .50 length; width under .80 length; test widest at apical system; 



globiferous pedicellariae with long teeth around mouth of valves depressus. 



Nacospatangus gracilis. 



A. Agassiz, 1873. Bull. M. C. Z., 3, p. 189. 



Plate 145, figs. 85-39. 



There are neither ophicephalous nor rostrate pedicellariae, but tridentate 

 are fairly common, and both triphyllous and globiferous occur, and the latter, 

 though small are very characteristic. The valves (PL 145, figs. 35, 36) have a 

 broad base and a short, cylindrical curved blade, with the terminal opening sur- 

 rounded by half a dozen short teeth (PL 145, fig. 37), and measure .20-.25 mm. 

 in length. The tridentate are not very variable; the valves, (PL 145, fig. 39) 

 are about .17-.25 mm. long with the blade about one fourth as wide. The tri- 

 phyllous have very broad valves (PL 145, fig. 38) only about .05 or .06 nun. long. 



1 The name is spelled Nacospatagus in both the Challenger and Panamic reports and the error 

 has been often copied. 



