294 CARDIASTER 



perforated ovarial plates. Fig. 3 b gives a lateral view, showing the increased elevation 

 at the anterior third, and fig. 3 c shows the position of the vent with its oval periprocte 

 in the posterior border. PI. LXXI, figs. 4 and 5 are figures of this Urchin from the 

 Lower Greensand of the Isle of Wight. This species was first described by Professor 

 Edward Forbes in the ' Memoirs of the Geological Survey,' decade iv, in his notes on 

 British species of Cardiasters appended to his description of pi. ix. It was collected 

 from the Lower Greensand of Maidstone, and presented to the Royal School of Mines 

 Museum by Messrs. E. H. Bunbury and Professor Morris. The specimens were too 

 imperfectly preserved to be described. The one that forms the subject of our figure in 

 PI. LXVI belongs to the collection of the British Museum, and I understand it was 

 collected from the same rock and locality. 



The test is broad, cordate, and hemispherical, convex on the upper surface, and 

 inflated at the sides. The anteal sulcus is wide below and shallow in the upper part ; 

 the ambulacrum smooth in the middle, with a row of tubercles on each side of the angles ; 

 the pores are minute, remotely placed in oblique pairs ; the antero-lateral ambulacra are 

 narrowly lanceolate ; the poriferous zones contracted, and the pores are like fine slits set 

 wide apart ; the postero-lateral pair are about the same width but shorter than the 

 anterior pair. The surface of all the plates is covered with a minute, close-set granulation, 

 and at the anterior border a few irregular rows of larger tubercles are developed. The 

 back is gently curved towards the upper angle of the vent, which occupies the middle of 

 the posterior border (PI. LXVI, fig. 3 b, c, and PI. LXXI, fig. 4 d). 



The base is much distorted in most of the specimens, appears to have been flat and 

 had numerous rows of large tubercles set upon the central plastron, and the sides and 

 anterior portion. 



The mouth-opening is situated near the anterior border ; it is transversely oblong and 

 bilabiate (PI. LXXI, fig. 4 b), the peristome is, unfortunately, displaced in the specimens 

 that have come into my hands. 



The apical disc is small, consisting of four pairs of perforated ovarials and five per- 

 forated ocular places (PL LXXI, fig. 4 a ; PI. LXVI, fig. 3 a). 



The posterior border is small, narrow, and truncated (PL LXXI, fig. 4 d; 

 PL LXVI, fig. 3 c), and the vent opens in its upper portion. 



Affinities mid differences. — This species, originally proposed by Professor Edward 

 Forbes for an Urchin from the Lower Greesand of Maidstone, which he considered to be 

 distinct from any other species, is characterised by the following diagnosis : — " C. late 

 cordatus, subhemisphcericus, dorso rotundato, seriebus pororum omnibus angu&tis sub- 

 equalibus. The anterior sulcus is strongly marked and wide below. The back is gently 

 curved. The vent is medial in position as compared with its height. The poriferous 

 avenues are all remarkably narrow, and the hinder ones as broad as the anterolaterals. 

 The surface of the test is too imperfectly preserved to be described." Since the date of 

 this description several specimens have been found in the Lower Greensand at Atherfield, 



