BRISSOPSIS LYRIFERA. 355 



bulacral petals uniformly sunken, posterior ambulacra shortest. Tubercles 

 more closely crowded within the peripetalous fasciole ; four ovarian openings 

 close together, nearly central. The pores of the lateral ambulacra are so 

 arranged as to form equally distant longitudinal rows. The anal system is 

 nearly circular, slightly elliptical vertically, distant from the subanal fasciole, 

 with a row of large plates round the exterior edge, the largest plates near 

 the anal fasciole, the remaining part covered by small plates. The subanal 

 fasciole is elliptical, strongly concave towards the anal system, sending off an 

 indistinct branch to the peripetalous fasciole. The tubercles of the subanal 

 plastron are closely packed, the spines usually arranged in two tufts on each 

 side of the median line. There are but few tubercles in the prolongation of 

 the petals; they are also less numerous in the median interambulacral sjiaces, 

 where the test is frequently quite bare. The actinal plastron is very promi- 

 nent, and the whole actinal surface is crowded by large tubercles of uniform 

 size, largest near the actinostome. The bare ambulacral spaces are very 

 broad, particularly the posterior ones. Forbes says of its color when alive, 

 '• a red body with pale yellowish spines, the dorsal and postanal impressions 

 of a rich brownish-purple." 



The only difference to be traced, after a careful comparison, between Flor- 

 ida and European specimens, is the existence of a distinct branch of the 

 subanal fasciole extending round the anal system to the peripetalous fasciole 

 (PI. XIX. f. 4). In European specimens there are traces of this branch, but 

 it is not distinctly and sharply defined as in the Florida specimens. The 

 subanal fasciole seems, from all I can gather after an examination of Spatan- 

 goids in various stages of growth, the only one subject to decided changes, and 

 it is not remarkable that we should have in Brissopsis similar variations, in the 

 subanal fasciole, to those upon which Troschel has founded his genera Aba- 

 tus, Hamaxitus, and Atrapus, — changes which, in Brissopsis at least, are due 

 to different stages of growth. The character of continuity of the adjoining 

 pairs of ambulacra, which Desor assigns to Toxobrissus as a distinguishing 

 feature, becomes more and more apparent according to the size of the speci- 

 mens ; so much so, that we should place Brissopsis lyrifera, when young, in 

 Brissopsis, but when full grown it would most decidedly pass for a Toxobrissus. 



Young Brissopsis lyrifera, less than a quarter of an inch in length, are 

 cylindrical (PI. XIX. f. 1-3), the mouth having a flat, crescent-shaped edge 

 (PI. XIX. f. 3), the test truncated vertically at the posterior edge (PL XIX. 

 f. 2), surrounded by a prominent elliptical subanal fasciole ; the peripetalous 



