AGASSIZIA SCROBICULATA. 595 



comparison of the original specimens leaves no doubt of the identity of the 

 three so-called species described from the Pacific side of Central America. 



Test thin, ovoid ; apical system nearly central, slightly posterior, coincident 

 with the vertex ; outline from above elliptical, rounded anteriorly, slightly 

 truncated posteriorly ; greatest breadth of the test across the central part. 

 Anterior ambulacral furrow narrow, shallow, but little sunken near the apical 

 system, and flush with the test at the ambitus. Anterior lateral ambulacra 

 somewhat more sunken, extending to the ambitus. Posterior lateral ambu- 

 lacra short, petaloid, with wide poriferous zones, and narrow interporiferous 

 space, somewhat over half the width of the poriferous zone. Apical system 

 small ; genital openings close together. Peripetalous fasciole with a deep 

 re-entering angle in the posterior lateral ambulacra, from which it extends 

 parallel to the anterior petals, as far as the ambitus, makes a right angle, 

 and crosses in a slightly curved line the anterior part of the test; this 

 part of the fasciole is the broadest. The lateral fasciole arises above the 

 extremity of the anterior petals, extends nearly on the same level, slightly 

 concave upwards towards the anal system, forms a sudden angle, running 

 to a point from both sides below the anal sj'stem, so far on the actinal surface 

 as to form an indentation in the posterior part of the actinal plastron. The 

 anal system is transversely elliptical, large ; no anal plates are preserved in 

 any of the Museum specimens. The actinal surface is slightly convex ; near 

 the posterior extremity of the broad actinal plastron there is a short rounded 

 keel. The posterior bare ambulacral avenues are narrow, and do not extend 

 to the ambitus. The actinostome is anterior, transverse, narrow, with a promi- 

 nent posterior lip. The fact that the anterior row of pores, forming the 

 continuation of the anterior poriferous zones of the anterior lateral ambulacra, 

 stops suddenly near the actinostome, seems to show that in Agassizia it is 

 the whole of the anterior poriferous zone of the anterior lateral petals 

 which is obliterated. This structure exists already in the youngest speci- 

 mens I have examined. The tuberculatum is quite irregular ; the tubercles 

 of the actinal surface in the anterior part of the plastron are large, closely 

 packed, arranged in transverse oblique rows, forming a regular pavement, 

 diminishing gradually in size towards the posterior end. In the lateral pos- 

 terior interambulacra the tubercles are large, distant, decreasing slightly in 

 size towards the fasciole ; in the actinal part of the anterior part of the test 

 the tubercles are large, distant, diminishing gradually in size across the fas- 

 ciole as far as the apical system ; the tubercles adjoining the lateral anterior 



