TOXOBRISSUS I'ACIFH'US. 



193 



laerum, the fourth abactinal series of which is reduced to a single plate 

 (PI. Ill"), fig. .',). The oculars are irregularly pentagonal ; the odd ocular is 

 far the smallest. The anterior pair of oculars are in the angle separating 

 the lateral genital plates. The posterior pair abut against the posterior 

 genitals and flank a part of the madreporite (PL 105, fig. 5). 



The actinostome is covered by an upper row of large polygonal plates 



with two or three rows of smaller ones. 

 The labium is T shaped, it is wide near 

 the actinostome. Fitr. 280. 



50 mm. 



Fig 279. T. pacificus. 



50 mm. 



Fig. 280. Toxobeissus pacificus 



Toxobrissus differs from Brissopsis in the structure of the apical system, 

 the genitals of the last genus extending into the interambulacral areas 

 (PI. 102, fig. 7). The extremities of five of the ambulacral plates are in- 

 cluded in the anal fasciole of Toxobrissus (PL 105. fig. G), while only four 

 are so included in Brissopsis (PL 102, figs. ',?, !)). The labium of Brissopsis 

 (PL 102, fig. g) is also shorter and more T-shaped than in Toxobrissus. 



The apical system belongs to the type of Brissopsis lyrifcra, Fig. 278, 

 rather than to that of B. cohimbaris, but the arrangement of the apical 

 interambulacral plates of the odd interambulacrum shows at once the radical 

 difference existing between Toxobrissus and Brissopsis. 



From the above it is clear that Bittner 1 is correct in stating that 

 Toxobrissus and Brissopsis are not identical, as I had suggested, and that 

 we are justified, taking into account some recent and some of the younger 

 geological forms, in establishing genera based upon the coalescence of 

 ambulacra. Dames, 2 on the contrary, goes so far as to substitute Metalia, 

 as being the oldest name, for Brissopsis and Toxobrissus, owing to the con- 

 fluence of the lateral posterior ambulacra. 



1 Bittner, Verhandl. d. K. K. Geol. Reichsanstalt, 1891, p. 103. 



2 Dames, Palaeontog. XXV, 1878, p. 67. 



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