INFULASTER. 305 



Genus — Infulaster, Hayenow MSS., 1851. 



Caediastek, Forbes. 1852. 



Infulaster, JDesor (with diagnosis). 1858. 



ZITTEL. 1879. 



Test narrow, oblong, of an irregular ovato-cordate form. Anterior half very much 

 elevated, rising into a prominent vertex, situated nearly above the anterior border ; the 

 anteal sulcus narrow, deep, and directed obliquely downwards and backwards, with two 

 prominent angular borders, which rise above the upper surface. Plates smooth, covered 

 with very small granules ; a few primary tubercles near the vertex and at the sides, and in 

 the centre of the under surface ; a sub-anal fasciole is seen only on some fine specimens. 



Infulaster excentricus. Hose. PI. LXX, fig. 1, a — /•. 



Spatangus excentricus. Rose. Woodwai-d's Geo), of Norfolk, p. 27, pi. i, fig. 5, 



1833. 

 Cardiasteb excentricus, Forbes. Ann. Nat. Hist., 2nd series, vol. vi, p. 443, 1850. 



— — Forbes. Mem. of Geol. Surv., decade iv, pi. x, 1852. 



— — Morris. Catal. of Brit. Foss., 2nd ed., p. 73, 1854. 



Diagnosis. — Test long, ovato-cordate ; upper surface considerably elevated anteriorly 

 and declining much to the posterior border ; anteal sulcus deep, narrow subvertical ; 

 vertex very excentric ; posterior border obliquely truncated, forming a triangular space, in 

 which the periprocte occupies the upper angle. 



Dimensions. — Antero-posterior diameter one inch and eight tenths of an inch ; 

 transverse diameter one inch and four tenths of an inch ; height one inch and three 

 tenths of an inch. These are the measurements of the large specimen figured in PI. 

 LXX, most kindly given to me by my friend the late Mr. Rose many years ago for this 

 work. 



De.scrij)fiofis. — This singular Urchin has long been one of the greatest rarities of the 

 Norfolk Chalk. When viewed in profile it presents the singular form seen in PI. LXX, 

 fig. 1 c ; the high vertex nearly overhangs the anterior border, and the upper surface 

 slopes away at an angle of 30° towards the posterior border which is truncated obliquely 

 downwards and outwards, and imparts another odd feature to the test. 



