ECHINUS WALLISII. 265 



coronal plates less numerous (in specimens 50-60 mm. 

 h. d., about 18 interambulacral and 38-40 ambulacral in 



each column) tenuispinus. 



Test thin, rather fragile, low, v. d. less than .55 h. d.; primary 

 spines much longer than the slender secondaries; usually two 

 or more oculars reach the periproct; if all are excluded, one 



is very slightly so margaritaceus. 



Valves of globiferous pedicellaria; have a lateral tooth on only one side but 



that one is conspicuous armatus. 



Echinus Wallisii A. Ag. 



Echinus Wallisii A. Agassiz, 1880. Bull. M. C. Z., VIII, p. 77. 



Plates 93, fig. 32; 108, figs. 1, 2. 



The type of this species (PI. 108, figs. 1-2) has never before been figured. 

 The statement in the original description that the pairs of pores are in sets of 

 two was based on the examination of the abactinal part of a single ambulacrum, 

 which possesses this peculiarity. Examination of other ambulacra and of 

 another specimen shows that this is not a characteristic feature at all, but is 

 only seen clearly in one ambulacrum. It is interesting to note (as stated above, 

 p. 261) that in the affinis form of Echinus acutus the abactinal ambulacral plates 

 very commonly consist of only two elements. As already indicated it is by no 

 means clear that Wallisii is not the adult form of Alexandri or possibly a local 

 variety. As bearing on the point, it may be noted that : the two specimens 

 at hand are respectively 60 and 100 mm. in diameter, 35 and 55 mm. high. The 

 abactinal systems are 15 and 29 mm. across, while the actinostomes are only 

 15.5 mm. and 26 mm. Although the primary spines are all more or less broken, 

 it is evident that in the type they measured between forty and fifty millimeters. 

 They are slender and smooth and have about 24 longitudinal striations. The 

 secondaries are short, rarely exceeding 12 mm. and are very slender. They are 

 not abundant, but are scattered over the test, with a fair degree of uniformity. 

 The test itself is very stout and rough, especially in the smaller specimen. The 

 roughness is due to the elevation of the tubercles and the depression of the 

 sutures. At and below the ambitus, each ambulacral plate carries a normal 

 primary tubercle, but above the ambitus, the tubercles are of irregular size and 

 occurrence. They are not so large as those of the interambulacra but they 

 cover a large part of the plate. The pores are large and the poriferous areas 

 quite broad. In the smaller specimen there are 26 ambulacral, and 16 inter- 

 ambulacral plates while in the larger specimen the figures are 28 and 20 respec- 



