242 ROBERT TRACY JACKSON ON ECHINI. 



dorsally, as seen in Plate 1, fig. 2, but a periproctal plate separates genitals 2 and 3 and others 

 separate genital 5 from 4 and 1 on either side. They thus present a certain bilateral symmetry, 

 but this may be only a coincidence. All the genitals bear a tubercle excepting genital 2, where 

 it is probabh' worn off, but if madreporic pores existed in 2, that might account for the absence 

 of a tubercle. The small relative size of the genitals and their position dorsal to the oculars 

 suggests a comparison with the somewhat similar condition in embryonic Echinus as seen in 

 Plate 3, fig. 5. 



The periproct contains nine or ten minute angular plates, the sutures of which are difficult 

 to make out, but apparently are as shown in the figure. They are similar to plates seen in 

 other Palaeozoic periprocts and present no striking feature (p. 174). 



Teeth, or more probably, dental pyramids exist in areas I, II, IV, and V. Jaekel considered 

 them parts of the dental system, and I agree with him, but Bather differs because of their radial 

 position. No other known structure occurs at this area in Echini, and their position, it seems, 

 may be accounted for by a possible accidental twist, as a considerable twist is occasionally 

 found in dried Recent material. To accept a radial position as normal in this type is opposed 

 to morphological principles, and in so far I should entirely support Bather's opinion. 



Bothriocidaris pahleni Schmidt. 

 Plate 1, figs. 3-6; Plate 8, fig. 1. 



Bothriocidaris pahleni Schmidt, 1874, p. 38, Plate 4, figs, la-lg; Zittel, 1879, p. 481, text-figs. 339a-339c; 



A. Agassiz, 1892, p. 72, Plate 29, fig. 1; Jaekel, 1894, p. 246; Jackson, 1896, pp. 233, 238, text-fig. 4; 



Gregory, 1900, p. 300, text-figs. 1-3; Lambert and Thie'ry, 1910, p. 118. 

 Botriocidaris pahleni Neiimayr, 1881, p. 152, Plate 1, fig. 6. 

 Botryocidaris pahleni Loven, 1883, p. 57, 2 text-figs. 

 Bothriocidaris palheni Pomel, 1883, p. 117. 

 Bothriocidaris phalcni Klem, 1904, p. 15. 



The test is small and nearly spherical; according to Schmidt, the type is 15.5 mm. in height 

 and 16 mm. in diameter. Ambulacral plates are high, hexagonal. Schmidt says there are 

 ten plates in a column, and eliminating the two peristomal rows, we have, therefore, eight 

 ambulacral plates in a column in the corona, as in B. archaica. The individual ambulacral 

 plates at the ambitus are 3 mm. wide and 2 mm. high. The pits for pore-pairs are about 0.5 

 to 0.75 mm. broad, showing two pores which are superposed. There are two tubercles to a 

 plate, and some of the spines are in place. They are longitudinally striate, up to 4 mm. long 

 and about 0.5 mm. thick; these are the only spines known in the genus. The interambulacral 

 plates are of the same height as the ambulacral, but narrower, 2.5 mm. wide at the ambitus. 

 The primordial interambulacral plates are pentagonal, ventrally in contact with the dorsal 

 border of the second row of peristomal ambulacral plates. The youngest plates dorsally against 

 the apical disc are pentagonal, or so low that they are nearly triangular. There are eight or 



