LARVIFORM CRINOIDS 



31 



Wanner is of the opinion that this group of crinoids forms a degenerate 

 series which developed from more complex ancestors by the partial or com- 

 plete atrophy of the radials and arms, displacement of the anal opening from 

 its normal posterior position toward one of the neighboring radii or completely 

 out of the dorsal cup of the crinoid, and displacement of the oral plates from 

 their original interradial position to a more or less perfectly radial position. 



Our Pennsylvanian collections contain a group of small crinoids whose 

 characters ally them to the Hypocrinidae. They are assigned to Lagenio- 

 crinus de Koninck and Le Hon and the three new genera Am pliipsalid ocrinus , 

 TytthocrinnSj and Dichostreblocrinus. Their relations and their probable 

 evolution is shown in the diagram (Fig. 4) of a portion of the Hypocrinidae 

 which is modified after Wanner [17, p. 98]. 



Genus LAGEN I OCRINUS de Koninck and Le Hon 1854 

 Genotype Lageniocrinus seminulus de Koninck and Le Hon 



The genus Lageniocrinus was established upon a small species of crinoid 

 which is very rare in the Lower Carboniferous limestone of Vise, Belgium 

 [3, p. 187J. This crinoid is composed of three rings of plates which were 

 originally interpreted as a circle of three basals and two radial circles of five 

 plates each, forming a completely enclosed flagon-shaped body. It was 

 suggested that this small crinoid is transitional between the Platycrinidae and 

 the Blastoidea. Zittel regarded the upper ring of plates as arm joints [18, 

 p. 350] and this view was shared by Wachsmuth and Springer [13, p. 175] 

 who suggested that this crinoid was possibly a young stage of Synbathocrinus. 

 Later both Bather [1, p. 152] and Springer [9, p. 209] placed Lageniocrinus 

 in synonomy under Synbathocrinus. 



In a detailed discussion incidental to his description of the new genus 

 Embryocrinus, Wanner returned Lageniocrinus to an independent generic 

 standing, pointed out its very primitive character, comparing it to a larval 

 stage of the living Antedon and distinguished the upper circle of plates as 

 orals [14. p. 134]. 



More recently, Jakovlev has offered the opinion that the isolated speci- 

 mens of Lageniocrinus that have hitherto been found are simply abnormal 

 examples of other more common crinoids [6, p. 313]. This view resulted 

 from his study of a series of nearly a thousand specimens of Hcuiistrcptacon 

 abracliiatus from the Permo-Carboniferous of the Ural Mountains among 

 which he found one example similar in structure to Lageniocrinus but appar- 

 ently connected by intermediate stages with Hcmistreptacon. 



Six specimens of a minute crinoid which is constructed similarly to the 

 genotype of Lageniocrinus, all obtained from the same locality, are of ap- 

 proximately similar size and must be regarded as mature individuals for they 



