344 THE FOSSIL ECHINOIDEA 



transversely. The anterior ambulacrum is not petaloid ; it is in a slight groove and 

 the pores are but slightly distinct. 



The peripetalous fasciole is very slightly sinuous, is subelliptical and rather close 

 to the ends of the petals. The anterior and the antero-lateral interradia have large 

 tubercles on those portions which are within the peripetalous fasciole. The tubercles 

 are large, close, and sunk in deep scrobicules. The odd interradium and also the 

 ambulacra are nearly smooth or finely granular. Actinally the ambulacra are smooth 

 and only marked by the pores, which are distinct. In front of the anus in the median 

 line there is an oblong and subcarinate-shaped mass of granules. The interradia on 

 this surface are covered with large, close, and prominent granules. 



The mouth is situated at the anterior one fourth of the distance from the front to 

 the back of the test. The anus is marginal, the periproct large, angular upwards, 

 sub-oval, and elongate in the direction of the vertical axis of the test. In some 

 individuals the odd interradium is raised into the shape of a keel. 



Correct as this diagnosis is for the most part, yet there are several misconceptions 

 in it and there are some very important details omitted which would fix the species 

 very decidedly. These defects are not to be laid to the charge of the distinguished 

 French savants, but to the imperfect nature of their specimens. 



Shape. The shape is somewhat variable, and there are three types which clearly 

 belong to this species and which have slightly different shapes. Taking one of these 

 as the normal form (Plate LIV, Fig. 5), it may be described as long, low, and rather 

 broad, is generally ovoid, rounded in front except where there is a broad and shallow 

 marginal groove, broadest a little in front of the centre and on a line with the apical 

 system, the same breadth extending backwards for a short space and then gradually 

 diminishing until a decided posterior truncation is reached, so that there is a nipping 

 in behind, especially posteriorly to the ends of the posterior ambulacra. The margin 

 of the base is rather sharply curved, and immediately above, the test is tumid in the 

 anterior regions, almost vertical, for a little height on a level with the posterior 

 ambulacra, sloping more gently along the course of the posterior ambulacra 

 to the side of the truncation, and finally truncated posteriorly, for the depression 

 in which is the periproct, the surface looking backwards and downwards. The 

 front of the test rises, on either side of the broad anterior sulcus, in a somewhat 

 sudden manner, and after being vertical, slopes with a very broad curve to a comparatively 

 flat area, with a very slight ascent posteriorly and behind the apical system. This 

 gentle slope persists to about one third of the distance from the apical system to the 

 edge of the truncation, but the slope then commences to be in the opposite direction 

 and is a little more decided than in front. So the highest point of the test is behind 

 the apical system, the antero-posterior curvature after the dorsal surface has been 

 reached being slight. There is some slight angularity of the margins of the test, and 

 the slight lateral swellings which produce them are one on the edge of the anterior 

 interradium, just behind the faint keel of the side of the sulcus ; another on the lateral 

 interradium close behind the line of the anterolateral ambulacrum ; and the third still 

 further behind and at the spot whence the slope towards the truncation takes its rise 



