Cystechinus crassus , a new Species from the Radiolarian Marls of Barbados, and the Evidence it affords as to the Age and Origin of those Deposits

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Abstract
The most important addition made by the ‘Challenger’ to our knowledge of the living Echinoidea was unquestionably the discovery of those abyssal Spatangoids which are Ethmophract, Meridosternous, and Adete; it was the close resemblance of these to the Cretaceous Ananchytidæ that led to the well-known and oftrefuted generalization that we are still living in the age of the Chalk. The discovery of a new species of Cystechinus , one of the most typical of these genera, in the Radiolarian beds of Barbados is therefore of interest; and this is enhanced by the light it throws on the age and horizon of those well-known deposits. Of the genus Cystechinus Prof. A. Agassiz has only given a comparative diagnosis; in the original description he simply states that it has the general appearance of Ananchytes , the simple ambulacral system of the Pourtalesiadæ, and an actinostome less labiate than in that group. He points out that it serves, with the genera Homolampus and Palæotropus , as a transition from the Spatangidæ to the Nucleolidæ and Echinolampidæ. In the ‘Challenger’ Report this notice has been somewhat expanded. Here the Galeritic features of the subcentral actinostome and the position of the anal system, the Ananchytid apical disc, the simple pores, the rudimentary auricles, and the proportions of the coronal plates in the ambulacral and interambulacral areas are all noticed.

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