NACOSPATANGUS. 



17 



Fig. 13. 



shorter-stemmed pedicellarioe with a smaller head ; the latter occur over the 

 whole of the actinal and abactinal part of the test ; the former are found 

 mainly in the broad, bare, posterior, actinal ambulacral avenues. 



The anal system is circular, covered by irregularly concentric plates, 

 diminishing in size towards the anal opening ; they carry secondary tubercles. 

 Anal opening nearly central, slightly protruding. The ambulacral tubes of 

 the petaloid portion of the ambulacra are lobed 

 {Fig. 1.3). The tubes of the phyllodes resemble 

 those of Echinocardium, terminating in club-shaped 

 processes {Fig. 14), strengthened by simple, curved, 

 limestone rods. In the base of the tubes the spi- 

 cules are, as in all Spatangoids, most irregular in 

 shape {Fig. 15). The details here given show the 

 correctness of the views of D'Orbigny and Cotteau 

 regarding the affinities of Asterostoma. Agassiz, 

 in the Catalogue Raisonne, leaves its position 

 doubtful, though acknowledging the affinities with Ananchytes, and places 

 it temporarily with the Cassidulidae. Desor, in his Synopsis, places the 

 genus among the Galeritidae, near Pachyclypeus. The genus Asterostoma 

 is known as a fossil from Cuba, and it is interesting that its nearest ally 

 should have come from the Barbadoes. 



100 fathoms, off Barbadoes. 



(SPATANGUS). NACOSPATANGUS. 

 Nacospatangus A. Ac, 1873, Bull. M. C. Z., ITT. p. 189. 



This subgenus is intermediate between Maretia and Micraster. The abac- 

 tinal part of the anterior poriferous zone of the anterior lateral ambulacra is 

 obliterated ; what there is left of the anterior zone is reduced to simple pores, 

 as in the extension of the zone beyond the petals towards the actinal surface 

 in Spatangoids generally. Agassizia is the only Spatangoid genus in which 

 the anterior zone is wanting, though in many Spatangoid genera — Echino- 

 cardium, Lovenia, Spatangus, Maretia — the abactinal part of the petals of the 

 lateral ambulacra is more or less rudimentary or irregular. The lateral pos- 

 terior ambulacra resemble those of Maretia. The anal extremity of the test 

 is that of Spatangus proper. The tuberculatum of the test, as in Micraster, 



