44 THE FOSSIL ECHINOIDEA 



tumidity of the ambulacra produces the peculiar marginal outline. Below, the test is 

 slightly concave. 



Apical system wanting. The peristome is rather large, slightly pentagonal, and 

 the cuts are distinct. 



The ambulacra, about one half of the breadth of the interradial areas, have three 

 pores in a slight depression arranged in simple vertical series, about four being in relation 

 to an interradial plate. There are three poriferous plates to each whole compound ambu- 

 lacra! plate, and the sutures are very distinct. The adoral poriferous plate is short and 

 band-like, extending the whole length of the ambulacral plate ; the median plate tapers 

 wedge-like inwardly, and is not more than two thirds of the breadth of the column ; and 

 the aboral poriferous plate is large, and might from its shape be compared to the 

 primitive plate of an echinid ambulacrum. The plates are placed rather obliquely, and 

 are more or less granular. Near the apex there is one small primary on each of the 

 larger plates ; near the ambitus there are two ; and close to the actinostome there is but 

 one, and it is larger there than elsewhere. 



In the interradial areas the median depression is evident, and the broad and rather 

 low coronal plates show sutural grooving, and near the angle the appearance of a slit- 

 like pit. 



At the ambitus the ornamentation consists of three small primaries or scrobicules 

 surrounded by miliary granulation, which partly forms circles around the areas, and a 

 confused intermediate ornamentation. Abactinally the number of primaries on each 

 plate diminishes until only one is seen ; and actinally they also diminish in number, 

 become larger until close to the peristome, and have distinct scrobicular circles. 

 Extending from these larger primaries on the actinal surface to some small primaries 

 near the pores are zigzag ridges. 



The tubercles of the interradial plates have a flat boss and small mamelon, and 

 are imperforate and non-crenulated. The cuts have a raised elongate ridge around 

 them. 



Height of the specimen -^ inch, breadth ^^ inch. 



Locality. Uncertain ; but the colour and nature of the fossilization indicates the 

 dark-brown Eanikot limestone. Survey-number G flf • 



Illustrations of the Swedes in Plate X. 

 Fig. 1. Progonechinus Eocenicus, Duncan and Sladen : natural size. 



2. Part of an ambulacrum and interradium near the ambitus : magnified. 



3. Part of an interradial area near the actinostome : magnified. 



4. Side view : natural size. 



Remarks. This species is interesting as presenting a link between the Diadematidee 

 and Echinidse (Triplechinidse). The structure of the ambulacra is essentially that of 

 the former group, whilst the tuberculation and general facies is very suggestive of some 

 of the fossil forms of PsammecUnus. Although the specimen under notice accords 



