SOME WEST INDIAN ECHINOIDS. 7 



examples both with an end tooth and without occurring even in the same specimen, 

 and this fact was especially urged as an argument against the value of the pedi- 

 cellarife in the classification of cidarids as set forth by me in the Ingolf Echinoidea. 

 In The CitlaridiB Doctor Clark figured a specimen of Tr. hartletti, which, as he 

 later informed me, was the specimen in which the various forms of pedicellarise 

 figured in the above quoted memoir (Plate 12a, figs. 6-13) were found. Now this 

 specimen differs through its spines so much from the typical form of Tr. hartletti that I 

 have suggested (Echinoiden der deutschen Siidpolar Expedition, p. 47) that it may 

 be a hybrid between Tr. hartletti and Stt/locidaris affinis; the argument detluced 

 from it against the classificatory value of the pedicellariie would therefore be 

 invalid. The correctness of this suggestion is discussed on page 10. 



Thus rmis the intricate history of this species. Though it has been so much 

 discussed, as yet no adequate description or sullicient figures have been given of it. 

 I thus naturally wished to take the opportunity here to give the description and 

 figures wanted and, accordingly, two specimens were sent to me together with 

 photographs of the largest specimen in the U. S. National Museum (Plates 2-3). 

 The Museum of Copenhagen hail previously received a small specimen of the species, 

 which has also been made the object of study on this occasion. The following 

 description is thus based mainly on these three specimens; but, of course, my 

 notes on the specimens examined during my visit to Washington and New Haven 

 are also taken into account. 



Measurements. 



The test is rather low, the height 54-59 per cent of the horizontal diameter; 

 the abactinal side is rather flat, the apical system only slightly elevated; the 

 sides are beautifully arched; the edge of the peristome not incurved. 



The ambulacra (Plate 14, fig. 9) are of the usual width, distinctl}' sinuate; 

 close inside the primary tubercle each plate carries a small secondary tubercle at 

 the lower edge, antl between these two a very small miliary tubercle (carr\"ing 

 pedicellarise) is generalty found; the rest of the plate is naked, and there is thus a 

 comparatively broad, wholly naked median space. In the largest specimen in the 

 U. S. National Museum (68 mm. horizontal diameter) a small third tubercle has 

 appeared inside the second on some of the ambulacra! plates at the ambitus, but 

 the naked median space remains as conspicuous as in the younger specimens." On 

 about 12-15 of the upper ambulacral plates as yet only the priniaiy tubercle has 



o The figures (Plates 2-3) do not show this, of course; a figure of the specimen in side view alone 



could ghow this feature. 



