GROWTH-STAGES OF THE BLASTOID, OROPHOCRINUS 

 STELLIFORMIS 



F. A. BATHER, F.R.S. 

 British Museum (Natural History), London 



The references to literature are given in the List of the Genera 

 and Species of Blastoidea in the British Museum, 1899. 



Among the specimens entered in that List are some referred by 

 Etheridge & Carpenter to Orophocrinus stelliformis (E840 and 

 E 1055), which, however do not agree well with the description by 

 those authors or with the original figures of the species, but seem 

 to agree more nearly with the form which Etheridge & Carpenter 

 distinguish as var. campanulatus Hambach. 



A set of sixteen specimens collected by Mr. D. K. Greger in 

 the Lower Burlington Limestone at White Ledge, Marion Co., 

 Missouri, and presented to the British Museum in 1918 by the 

 late Dr. G. B. Longstaff (E30091-30106), if arranged in order of 

 size, shows a complete transition from the campanulatus form to 

 the typical stelliformis, the latter being the larger. The dozen or 

 so specimens previously in the museum fit into their places in this 

 series. There can therefore be no doubt that the alleged species 

 or variety O. campanulatus is merely the young of O. stelliformis. 



Apart from mere size the growth-changes consist in: 



1. An increase in the greatest diameter as compared with the 

 height of the theca. 



2. The lowering of the ambitus from a position but little below 

 the oral pole to one less than half the height of the theca from the 

 base. 



3. A consequent change from a tumbler outhne, through a 

 bell outhne, to a parachute outline, the sides changing from straight, 

 or in part convex, to concave, and the summit changing from almost 

 flat to flattened-convex or convex. 



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