SPATANGUS PAUCITUBERCULATUS. 237 



Spatangus paucituberculatus. 



A. Agassiz and Clark, 1907. Bull. M. C. Z., 50, p. 253. 



Plates 146, fig. 19; 157, figs. 7-9. 



Length 78 mm. or 73 mm. if the measurement is taken in the mid-line where 

 ambulacrum III is so deeply depressed; width 74 mm.; height barely 40 mm. 

 In nearly all the specimens the sternum is crushed in, preventing accurate meas- 

 urement of the height, but there is no doubt that some were not half as high 

 as long; some were almost or quite as wide as long. The form of the test, the 

 tuberculation, the form of the petals, the position and shape of the subanal 

 fasciole, the form and tuberculation of the sternum, and the narrow, curved, 

 ventral ambulacra are all better understood from the photographs (PI. 157, figs. 

 7-9) than from any description. The apical system is markedly anterior and 

 the four genital pores are very close together. Only three ambulacral plates, 

 with two large tube-feet, enter into the composition of the subanal plastron on 

 each side. The periproct is 9 mm. wide by 7 mm. high and is situated just 

 below the upper margin of the posterior end of the test. Below the periproct 

 the test slopes obliquely towards the mouth, but the convexity of the subanal 

 plastron tends to obscure this obliquity. The peristome is very deeply sunken 

 and so far overhung by the labium that it hardly shows in the photograph (PI. 

 157, fig. 9). The color is purple with white tubercles; primaries and secondaries 

 silvery white becoming purple at base ; miliary spines purple. 



The covering of spines is rather dense; the miliaries are only about a 

 millimeter long but most of the secondaries are 3 mm. and the smaller primaries 

 5-7 mm.; the largest primaries, in the posterior interambulacra are 12-15 mm. 

 long. Pedicellariae are not very common and no globiferous, ophicephalous, 

 or rostrate were found. The triphyllous pedicellariae have valves about .14 mm. 

 long. The slender tridentate are not at all peculiar; the valves are 1.00-1.20 

 mm. long. The stout tridentate, with valves .45-.60 mm. in length, have the 

 blade somewhat pointed, but the sides are convex and not straight, so the out- 

 line (PL 146, fig. 19) is not triangular. 



It is a remarkable fact that the nearest ally of this Hawaiian Spatangus is 

 the recently described species, inermis, from the Mediterranean (see p. 238). 

 It differs in the more flattened test, the more deeply sunken peristome, the 

 presence of a few primaries in interambulacra 1 and 4, the more oblique subanal 

 plastron and the shape of the valves of the stout tridentate pedicellariae. 



