from the Lias and Oolites. 317 



pentagonal ; the anal plates form a narrow prominent ring at the 

 vertex, and the interambulacral areas are in general divided by a 

 median depression. 



Polycyphus nodulosits, Miinster. 



Syn. Echinus nodulosus, Goldfuss, Petrefact. Ger. tab. 40. fig. 16 ; 



Agassiz, Cat. Syst. p. 12. 

 Arbacia nodulosa^ Agass. Prodrom. 

 Polycyphus nodulosus, Agass. & Desor's Cat. raisonn^, Ann. Scien. 



Nat. tome vi. p. 361. 



Test hemispherical; ambulacral areas a little more prominent 

 than the interambulacral areas ; ambulacra with from four to 

 five rows, and interambulacra with from twelve to fourteen 

 rows of small tubercles disposed in nearly parallel lines ; bases 

 of the ambulacra with twelve, those of the interambulacra 

 with sixteen larger tubercles. 



Height /oths of an inch, diameter ^^ths of an inch. 



This pretty little Urchin was first described by Prof. Goldfuss 

 from specimens named by Count Miinster from the Oolites of 

 Baireuth ; the hemispherical test exhibits a disposition to assume 

 a subpentagonal circumference from the greater prominence of 

 the ambulacral areas ; the surface of the test is divided into 

 fifteen nearly equal lobes by the ten poriferous avenues, and the 

 five depressions which divide the interambulacra down their 

 mesial lines ; these lobular divisions are more defined in young 

 and small specimens than in large and old ones ; the ambulacral 

 areas are one half the width of the interambulacral, and have 

 nine large tubercles at their base, and four or five rows of small 

 tubercles at their widest part, which gradually diminish to three, 

 two and one as we approach the apex of the area ; the interam- 

 bulacral areas are twice the width of the ambulacral, they have 

 about twenty-four large tubercles at their base, and about twelve 

 rows of small tubercles at their widest part, which gradually 

 diminish by the disappearance of the external rows to ten, eight, 

 six, four and two, as we trace the rows from the equator to the 

 apex of the areas ; the tubercles on the sides and upper surface 

 of the test are nearly of a uniform size, they are arranged in 

 rows, the tubercles are opposite each other and do not alternate 

 as in some other genera. The interambulacral areas are each di- 

 vided by a slightly depressed line into two lobes ; these are sepa- 

 rated from the ambulacral areas by straight narrow poriferous 

 avenues, so that the test of this beautiful Urchin appears to con- 

 sist of fifteen nearly equal lobes, those of the ambulacra being 

 the most prominent and best defined, in consequence of the 



