U THE TEKTIAEY FOSSIL ECHINOIDEA 



bare, having a few scattered rounded granules on it anterior to the posterior margin. 

 The openings for pores are few in number. 



The interradia are tumid abactinally from before backwards. The anterior 

 portion of the test is marked by the excavation of the broad and moderately deep 

 groove at the ambitus, and there are two slight vertical projections on each side 

 of the groove, which are well defined by a slight gibbosity on each plate. 



The lateral interradia are tumid around the apex, and, as this condition is noticed 

 in the others, the apical system is in the midst of a slight depression. The posterior 

 interradium is narrow and long, convex from side to side and from before backwards ; 

 it forms a well-rounded tumid mass between the posterior ambulacra, is pinched in a 

 little on either side between their ends, and is broadly truncated posteriorly, the slope 

 looking backwards and downwards obliquely. There is a swollen look about the 

 interradium at the margin, and also actinally on either side of a shallow groove 

 below the periproct. The plastron is long, triangular, and has a slight central keel 

 placed longitudinally and reaching two thirds of the distance to the mouth. The 

 plastron is slightly convex from side to side. 



The peristome is excentric in front and rather close to the anterior margin ; it has 

 a well-defined arched posterior lip, which is covered with small tubercles and granules. 



The periproct is large, broadly elliptical, its greatest diameter being in the vertical 

 direction, and it is rather pointed above and below. Below it is a shallow broad groove. 



There are two fascicles — a peripetalous, which is very narrow and which runs a 

 rather irregular course ; and a subanal, which is a little broader than the other. 



The peripetalous fasciole is broadest below the posterior poriferous zone of the 

 antero -lateral ambulacra, with which it is not in contact, being 5 millim. nearer the 

 margin than the last pair of pores. The fasciole then passes forwards and slightly 

 upwards to reach a gibbosity on the outer vertical low keel of the anterior interradium ; 

 it then passes downwards and towards the median line to the keel by the side of the 

 odd ambulacrum, and passing still towards the median line, it crosses the ambulacrum 

 with a broad curve, convexity downwards, just as the ambitus slopes towards the 

 base, and 19 millim. from the lowest point of the groove in the anterior part of the 

 test, and 40 millim. from the apical system. Behind the antero-lateral ambulacra the 

 fasciole turns suddenly but remotely, and then curves slightly into the area between the 

 ambulacra before passing downwards and backwards to reach the end of the postero- 

 lateral ambulacra, which it bounds ; it then crosses the posterior interradium, with a low 

 curve, convexity upwards. It consists of a ribbon-shaped narrow band marked with close 

 minute granules, and it is bounded by a single series of small low tubercles. ' 



The subanal fasciole includes the broad tuberosities on either side of "the groove 

 beneath the periproct, and it passes over the edges of this groove. Seven pairs of pores 

 of the postero-lateral ambulacra are just within its outer curve. 



The ornamentation of the test, abactinally, is difi^erent within the peripetalous 

 fasciole, and beyond it or nearer the margin of the test. Within the fasciole on the 

 lateral and posterior interradia there are a few definitely placed, and on the anterior 



