BRISSOPSIS COLUMBAEIS. 



191 



The Panamic Brissopsis l is readily distinguished from the Atlantic 

 species by the greater length of the posterior lateral ambulacra (PL 103, 

 fig. 3), the flatness of the test (PI. 100, figs. 6, 7), and the great width of 

 the area enclosed by the subanal fasciole (Pis. 100, fig. 7 ; 103, fig. 1). The 

 anal extremity of the test is more sloping (PI. 100, fig. 6) than in the 

 Atlantic species, and is characterized by the great size of the anal opening 

 (PI. 100, fig. 7); in older specimens the anal system increases rapidly in 

 size. The Panamic species is noted for a marked indentation of the test 

 at the lateral anterior ambulacra when seen from the actinal or abactinal 

 side (PI. 103, figs. J, 2) ; the great width of the posterior lateral ambulacra 



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Fie. 27S. B. lyrifeba. 



After Lov£n. 



and the large size of the ambulacral plates as compared with those of the 

 Atlantic species are striking features of the Panamic species. 



The apical systems of the Atlantic and Panamic species of Brissopsis 

 differ materially, that of B. lyrifera, Fig. 278, is more like that of Toxobrissus 

 pacificus, both showing the sutures of the genital plates, while in B. colum- 

 baris, Fig. 277, the sutures cannot be made out, and the madreporic genital 

 extends but little into the median odd interambulacrum, Fig. 277, scarcely 

 beyond the second apical ambulacral plate. In B. lyrifera it reaches to the 

 level of the seventh plate. Fig. 278, and in T. pacificus to that of the fifth, 

 Fig. 279. 



1 In the elongated and globular specimens of the West Indian Brissopsis lyrifera the structure of 

 the odd interambulacrum of the two types is identical, as well as that of the abactinal system. 

 Though there is a confluence of the posterior lateral ambulacra, the structure of the odd ambulacrum 

 is not modified as in the case of the Panamic Toxobrissus. So that, in spite of the elongated form 

 and confluent ambulacra of some of the West Indian specimens of Brissopsis, they cannot be referred 

 to Toxobrissus. 



