484 Mr. D. W. Devanesen. Develojwienf. of the Calcareous 



(5) Sollas, W. J. (1899). "On Silurian Echinoidea and Ophiuroidea," 'Quart. Jour. 



Geol. Soc.,' vol. 45. 



(6) Spencer, W. K. (1904). " On the Structure and Affinities of Palaodiscus and 



Agelacrinus," 'Roy. Soc. Proc.,' vol. 74. (1913 and 1917).— "A Monograph of the 

 British Palaeozoic Asterozoa,' : Palaeontographical Society. 



(7) Theel, H. (1892). "On the Development of EcM-nori/amiis pusiUus," 'Nova Acta 



Roy. Soc. Scieu., Upsala,' vol. 15. 



(8) TJbisch, L. V. (1913) "Die Entwicklung von Strmigyloeentrotm Hindus," ' Zeit. 



Wissen. Zool.,' vol. 106, Part III. 



EXPLANATION OF PLATES. 



List of Abbreviations used. 



A. Alveolus. 



B Boss of a spine. 



BK. Beak of a cone. 



B.L Basal ends of lamellae. 



CA Carina of a tooth. 



CP Calcareous particle — the starting point of a lamella. 



C 'OJf. Compass. 



J) Calcareous disc of a tube-foot sucker. 



E. Epiphysis. 



EL. if. Elevator muscles of a compass. 



F. Flange of a lamella. 



F.C. First cone. 



I.C. Inner rudiment of a compass. 



IN.M. Inter-pyramidal muscles. 



L Lamellae of a tooth. 



2L.C A pair of lamellae in the process of cone-formation. 



2L.C" A fully formed cone. 



O.C Outer rudiment of a compass. 



OE. CEsophagus. 



O.E. Offshoot of an epiphysis. 



O.T. Oral end of a tooth. 



P.E. A pair of epiphyses. 



Pi Rotula. 



R.A Rudiment of an alveolus. 



Ji.E. Rudiment of an epiphysis. 



JIT. Root-end of a tooth. 



R.R Rudiment of a rotula. 



SH. Shell. 



SP Spine. 



S.C. Suture between the two rudiments of a compass. 



S.E. Suture between the processes of two epiphyses. 



T. Tooth. 



As the six figures form a jjrogressive series, all <)f them should be consulted with 

 regard to any particular ossicle of the lantern of Aristotle. 



