MUSEUM OF COMPAKATIVE ZOuLOGY. 



175 



R. lofotensis (maximum.) 



N. B. — Pourtales described his largest specimen of R. lofotensis as having a stem 

 nearly 130 mm. long and composed of 59 joints, the length of which averages three 

 times their diameter. 



The stem-joints of R. rmvsoni are relatively shorter and thicker than 

 those of R. lofotensis, in which the length is three times the width. In 

 absolute size, as well as in the proportions of the basals and of the stem- 

 points, the " Porcupine " examples of this type are the ones which 

 approach R. lofotensis most nearly. They are smaller than those from 

 the Azores, which are themselves smaller than the Caribbean specimens, 

 a fact whioh is doubtless due to variations of temperature. The differ- 

 ence in size between the largest specimens of R. lofotensis found by Sars 

 and Pourtales respectively is likewise probably the result of the differ- 

 ence between the temperature of the Gulf Stream in the Florida Straits 

 and that of the Northeast Atlantic. It is noteworthy that an elongated 

 calyx resembling that of R. raivsoni is chiefly found in those individuals 

 of R. lofotensis which have the arms best developed ; * so that this spe- 

 cies probably represents a further stage in the degradation of the Apio- 

 crinite type than is reached by R. rawsnni. The occurrence of the 

 latter form in the Eastern Atlantic is of extreme interest, owing to its 

 remarkable resemblance to Bourgueticrinus londinensis. This type was 

 named by Forbes from some isolated stem-joints in the London clay ; 

 but a well-preserved calyx has since been discovered, whicli is now pre- 

 served in the Natural History Museum at South Kensington. 



Several species closely allied to B. londinensis, which occur in the Ter- 

 tiary deposits of France and Italy, are referred by Zittel f f^nd other 

 palaeontologists to the genus Conocriniis D'Orbigny ; e. g. C. jjyriformis 

 Miinst. sp., C thorenti D'Arch. sp., C. coraidus Schafh. sp., C. suessi 



* Sars, Crinoiiles Vivants, p. 4. 



t Palaeontologie, p. 392. See also Meneghini, "I Crinoidi Terziarii," Atti d. 

 Soc. Tosc, Vol.11, pp. 11-17. Schluter, " Ueber einige Astylide Crinorden," Zeitsch. 

 d. ilentsch geol. Gesellsch., 1878, pp. 52-55. De Loriol, "Crinoides fos.siles de la 

 Suisse," p. 190 ; and Paleontologie Fran9aise, "Terrain Jurassi(iue," Tom. XI. (1882), 

 p. 65. 



