PLATYCRINID.E — HEXACRINUS. 49 



Synonymes and References. 



Platycrinus interscapularis. — Pliill. Palaeozoic Fossils, PI. 14, fi(j. 39. 



Aust. Ann. Sf Mag. Nat. Hist. vol. 10, p. 109. 



Formation and Localities. 



Devonian strata. — South Devon ; Newton, and Plj'mouth. 



We have taken this species as the type of our proposed genus Hexncrinns, because it 

 lias been obtained in a fine state of preservation, and tlierefore furnishes clear evidence 

 of its character, and title to this distinction. 



The five perisomic plates which bear the rays are excavated at their upper edges to 

 admit the basal ray joints, in a similar manner to those of the Plfifi/crini. The sixth or 

 non-bearing perisomic plate, is irregularly hexagonal. All the plates are somewhat 

 thinner in proportion to their size than is commonlj^ observed in the Plalycriui. 



It is to be regretted that no specimen belonging to this genus, with any considerable 

 portion of the rays attached, has hitherto been discovered. 



Among the various portions of columns met with in the Devonian system of rocks, we 

 cannot with safety refer any one of them to heretofore known species ; and though Mr. 

 Phillips has named several from their supposed resemblance to those belonging to certain 

 genera, we consider it the safest course and less liable to create confusion and error, to 

 leave these fiagmentary specimens unappropriated, until more certain evidence is ob- 

 tained as to the genera and species to which they properly appertain. In order however 

 that their form may be known, we have represented several of them in our seventh plate. 



2. Species. Hexacrinus DEPRESSUS. (Austin-) 

 PI. VI. fg. 2, a, b, c, d, e. 



Definition — Dorso-central plate tripartite and hexagonal; perisomic plates six, five 

 of which bear the rays as in the typical species ; abdominal plates coverhig tiie apex 

 depressed instead of forming a dome, as in the first species ; small granulie are thickly 

 dispersed over the whole exterior of the plates. Mouth sub-central and unobtrusive ; 

 rays and column unknown. 



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