266 EPI ASTER 



backwards and inwards, and inclined at 30° ; posterior border obliquely truncated ; vent 

 large, oval, supra-marginal ; base convex ; mouth-opening in the anterior fourth ; peri- 

 stome bilateral. 



Dimensions. — Length, antero-posterior diameter two inches and five tenths ; breadth, 

 two inches and five tenths ; height, one inch and five tenths. 



Description. — This fine large ^piaster has been long known to geologists as a fossil 

 from the Upper Greensand of Wiltshire, as I have detected specimens in different 

 collections made many years ago. It was erroneously identified with Parkinson's 

 Spatangus lacunosus, which is a Maltese specimen, and was entered in the first edition of 

 Morris' Catalogue as Micraster lacunosus. It was omitted from the second edition of 

 that work, and described by Dr. S. P. Woodward as Hemiaster bucardium, from his 

 belief that it agreed with Goldfuss' figure. 



The test is large and cordiform in middle growth, and round and tumid with age, 

 when its width and length are about equal. The vertex is at a point between the 

 terminal portions of the postero-lateral ambulacra, from whence its horizontal profile 

 slopes gently towards the anterior border and backwards to the abruptly truncated 

 posterior border. 



The anteal sulcus is deep and narrow, with nearly vertical walls ; it grooves deeply 

 the anterior border, fig. 1 a, and extends from the disc to. the mouth, fig. 1 e. 



The pores are small, biserial, closely set together, and limited to the upper half of the 

 area, with a prominent granule between the two pores forming a pair. 



The ambulacra are much depressed, circumscribed, and unequal in length and 

 inclination ; the antero-lateral are one third longer than the postero-lateral pair. 



The poriferous zones are wide, of unequal length, and formed of transversely elon- 

 gated pores, those in the posterior zone of the antero-lateral pair are the longest and there 

 the pores are widest apart. 



There is no true peripetalous fasciole, and the naked line which Mr. Bone mistook 

 for this structure and figured as such appears to have been produced by friction on the 

 sutures of the large inter-ambulacral plates forming the peripetalous area added to a 

 certain local baldness at the terminal portions of the depressed ambulacra, so that 

 referring to Plate LIX the student must please delete the peripetalous naked line in 

 fig. 1 a, c, d, e, f ; in all other respects the various figures given on this plate are 

 admirable delineations of the form and structure of this fine Epiaster. 



The apical disc is central ; it has four perforated ovarial plates, a very small spongy 

 body, and five oculars with distinct orbits. 



The numerous small tubercles are arranged in rows in quincuncial order on the 

 plates and the interspaces are covered besides with abundant granulations. Fig. 1/ 

 represents three inter-ambulacral plates, the terminal portion of an ambulacrum, with 

 its poriferous zones, magnified three diameters in order to illustrate this portion of the 

 anatomy of the test. 



