74 THE VOYAGE OF H.M.S. CHALLENGER. 



Neocomian of Switzerland. The generic value of the type was doubted by Schliiter j 1 

 and I had formerly myself some hesitation in regarding it as equivalent to Antedon, 

 Actinometra, and Promachocrinus. 2 For there is no definite character, except the 

 simplicity of the rays, which can separate Eudiocrinus from the ordinary ten-armed 

 Antedon ; and in one of the three species of the ten-rayed Promachocrinus the rays divide 

 so as to form twenty arms (PI. LXX.), while in the two others there are ten undivided 

 rays (PL LXIX. figs. 5, 9, 10). But this character alone would hardly justify the 

 separation of the simpler type of Promachocrinus from the twenty-armed form ; while 

 I have an abnormal specimen of an Antedon with only nine arms, owing to one of the 

 rays not dividing, which is the case with all the rays of Eudiocrinus. 



Nevertheless, it sometimes happens that a character, which is only of specific value 

 in one type, may be of generic value in another. Five recent species of Eudiocrinus 

 are known, four of which range from Japan into the South Pacific Ocean (lat. 37° S.), 

 while one occurs in the East Atlantic, and another has been found fossil in the 

 Neocomian of Switzerland. The simplicity of the rays thus appears to be a character 

 of some morphological importance, and I am, therefore, disposed to admit the generic 

 position which was originally assigned to the type by Semper. Unfortunately, however, 

 it cannot continue to bear the name by which he described it. For Salter, fifteen years 

 before Semper's description of Ophiocrinus, had designated by the same generic name 

 an obscure Crinoid from the Devonian of South Africa ; and the confusion thus 

 existing was increased by the posthumous publication in the year 1878 of the late 

 Professor Angelin's monograph of the Swedish Silurian Criuoids, in which the name 

 Ophiocrinus is connected with a third and totally distinct type. 



Professor Semper's genus being thus preoccupied, I proposed in 1882 to call the type 

 Eudiocrinus (evStos, calm), in allusion to the fact that the four recent species of it, which 

 were then known, were limited to the Pacific Ocean. Curiously enough, however, a 

 few months before I suggested this name, several specimens of a new species of Eudio- 

 crinus were dredged by the French exploring vessel " Travailleur " in the Gulf of Gascony, 

 and, therefore, in European Seas. The type was naturally designated as Eudiocrinus 

 atlanticus by Professor Perrier, 3 who gave a brief description of the characters which 

 distinguish it from the Pacific species. 



Eudiocrinus, like Antedon, has a central mouth (PI. VI. fig. 2), and a more or less 

 hemispherical or conical centro-dorsal, an isolated specimen of which could not be 

 distinguished from the corresponding part of an Antedon (PI. III. fig. 7a; PL VI. fig. 1; 

 PL VII. figs. 1, 3, 4). The radials, however, in the only recent species which I have 

 been able to examine, differ slightly from those of the ordinary Antedon-type which is 

 illustrated on Pis. I. -IV. The articular faces are low relatively to their width (PL III. 



1 Zeitschr. d. deutsch. geol. Gesellsch., 1878, p. 4(1. s Quart. Journ. Gcol. Soc, 1879, vol. xxxvi. p. 41. 



3 Comptes rendus, 1883, t. xcvi. No. 11, p. 725. 



