ORAL AND APICAL SYSTEMS OF THE ECHINODERMS. 355 



difficult genus is the correct one, but with regard to 

 Hagenow's Hertha mystica I have no hesitation in saying 

 that the five triangular plates forming the so-called pyramidal 

 " roof" are not in any way homologous to the oral valves of 

 the pre-brachial Comatula, as suggested by Allman. 

 ' Miiller's^ determination of them as parts of the (first) radial?, 

 which remain attached to the centrodorsal piece is un- 

 doubtedly the correct one. In the same Avay I am convinced 

 that the five pieces forming the pyramidal "roof" of Eu- 

 gemacrmus caryophyllatus are not in the least to be 

 regarded as an " oral series," but that Quenstedt- was 

 perfectly right in describing them as forward processes 

 between the two distal articular surfaces of the third or 

 axillary radials. They are, in fact, homologous with the 

 " clavicular piece " of Schultze," which occurs also, though 

 developed to a far less extent, on the radial and brachial 

 axillaries of Acti?iomet7'a polymorplia. 



Among the recent Crinoids the oral plates of the Penta- 

 crinoid larva appear to have a very difierent fate, according 

 as the adult animal remains throughout life in the pedun- 

 culate, and therefore embryonic, condition, or is set free from 

 the stem at the end of its development. In the latter case, 

 as exemplified in Comatula, the orals undergo a gradual re- 

 sorption, which commences before the termination of Penta- 

 crinoid life, and is completed very soon after the young 

 Comatula has entered upon the free stage of its existence. 

 On the other hand, in some, though not all, of the recent 

 genera of pedunculate Crinoids, the oral plates of the larva 

 persist through life, supporting the oral valves in the inter- 

 radial areas of the disc. Sars^ and Ludwig-^ have met with 

 them in Rhizocrinus ; and Wy ville Thomson^ finds them in 

 Hyocrinus, though not in Bathycrinus. 



He has also described them in the remarkable genus 

 Holopus^ as five rather large triangular plates which meet in 



' " Ueber den Bau des Pentacrinus caput Medusts'^ ' Abhandl, der 

 Berlin Akad. 1843/ p. 28. 



-. "Ueber Eugeniacrinites cari/ophyllatus" 'Neues Jahrbuch fiir Minera- 

 logie, 1855/ p. 671. 



^ " Monographie der Echinodermen des Eifler Kalkes/' p. 5. ' Denk- 

 schriften der Wiener Akademie/ Bd. xxvi. 



* "Metnoires pour servira la connaissance des Criuoides vivanls." ' Du 

 Rhizocrinus lofotensis/ p. 17. 



'" " Zur Anatomie des Rhizocrinus lofotensis," ' Zeitschr. fiir Wiss. Zool./ 

 Band xxix, p. 115. 



'' " Notice of new living Crinoids belonging to the Apiocrinidee," ' Journal 

 of the Linnean Society, Zoology/ vol. xiii, pp. 51 — 53. 



" " On the Structure and Relations of the genus Holopus," ' Proceedings 

 of the Royal Society of Edinburgh/ vol. ix, p. 409. 



