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ECHINOCONUS 



The vent is elliptical (fig. 2 d) ; one third larger than the mouth in vertical dimensions ; 

 it is placed at the lower part of the posterior border in the single ambulacrum imme- 

 diately below the margin (fig. 2 b), or just within the range of the same ; it varies a little 

 in the degree of its elevation in the different specimens I have compared. 



Affinities and Differences. — This species is distinguished from its congeners by its 

 elongated and pentagonal form ; it is enlarged anteriorly and tapers slightly posteriorly, 

 its greatest transverse diameter being across the antero-lateral ambulacra ; it becomes 

 a little narrower towards the posterior border, which is rounded with an elongated ridge 

 rising from the upper angle of the elliptical vent. The primary tubercles of both areas are 

 of the same size ; they are sunk in areal depressions and scarcely rise above the general 

 surface of the plates, the whole of the intermediate structure being covered with numerous 

 close-set granules ; so that the shell of Echinoconus castanea feels smooth to the touch 

 when compared with that of Echinoconus conicus or E. abbreviates. In this respect it 

 resembles E. subrotundus ; the latter, however, has a smoother test, with fewer and 

 smaller tubercles on the plates ; besides this character the elongated pentagonal form 

 is very characteristic of E. castanea. 



Locality and Stratigraphical Position. — Echinoconus castanea is collected very rarely in 

 the Upper Greensand. A few specimens have been found in this formation at Chute Farm, 

 near Warminster, and one of these now lies before me. Small forms of this Urchin in 

 fine preservation are very characteristic of the Chloritic Marl near Chard, a bed of Chalk 

 Marl tinged green with scattered particles of silicate of iron, which lies between the Chalk 

 Marl and Upper Greensand, and contains a most interesting suite of Echinidce, all of 

 which likewise occur in the Upper Greensand formation. The large figured specimen 

 was obtained from the Chalk Marl near Lewes, in Sussex. I have others that were 

 collected from the bed of hard gritty Lower Chalk near "Folkestone, a stratum which has 

 yielded many interesting Urchins, as Salenia granulosa, Cyphosoma simplex, and numerous 

 Polyzoa. It belongs, therefore, to the lower division of the Cretaceous formation. 



Foreign Distribution. — It was collected by Mr. Alex. Brongniart in the Albien stage 

 of the Chalk at the Mountain of Fis, in Savoy ; in the same stage near Nice, by M. 

 Cailliaud ; in France at Escragnolles (Var), by MM. Cotteau and Kcechlin ; near Pros, 

 Valley cle Rencurel, near Grenoble (Isere), by M. Albin Gras. 



