REPORT ON THE CRINOIDEA. 269 



The number of ambulacra reaching the peristome was thus the sole character by which 

 Miiller proposed to separate Actinometra from the majority of the Comatulse then known 

 to him ; and the discovery that five symmetrically distributed ambulacra might converge 

 on an excentric mouth led him to regard the grouping of the ambulacra as a character of 

 less systematic value than he had previously attributed to it, so that the name Actinometra 

 was reduced from generic to subgeneric rank. 



It is curious that Miiller should have attached so much importance to the number of 

 ambulacra converging on the peristome, and so little to the excentric position of the 

 mouth and the accompanying enlargement of the anal interradius which he had described 

 so clearly. For whether the number of primary ambulacra be three, four, or five, as he 

 figured in Comatula Solaris, Comatula waHbercji, and Comatula multiradiata respectively, 

 the mouth is always excentric, and the anal tube in the middle of the horseshoe-shaped 

 curve formed by the two posterior ambulacra. The Comatula multiradiata which he 

 figured 1 was not the dry Eetzian type bearing this specific name which he had already 

 referred to Actinometra, but a spirit specimen in the Paris Museum which had been 

 identified with the Comatula multiradiata of Lamarck. It has an excentric mouth, 

 but five primary ambulacra which Miiller described as distributed symmetrically to the 

 different groups of arms, 2 and it was therefore referred by him to the subgenus Alecto. 

 Except as regards " die Bildung des Scheitels," however, his specific description of Alecto 

 midtiradiata was simply a reproduction of that which he had given of the dry Asterias 

 multiradiata, Retzius. He had stated expressly that this showed the same horseshoe- 

 like distribution of the ambulacra as his type species of Actinometra ; and his subsequent 

 reference of it to Alecto is therefore difficult to understand. The number of Actinometra 

 species thus became reduced to three, viz. — (l) the type, Comatula {Actinometra) Solaris, 

 Lam., sp., with which Miiller was inclined to unite Asterias pectinata, Retzius; (2) 

 Comatula {Actinometra) ivahlbergi, Midi.; and (3) Comatula {Actinometra) rotalaria, 

 Lam., sp. All three of these had been previously referred by Midler to Alecto, which 

 name he used in place of Comatula, Lamarck, as being one of older date ; but when, 

 later on, he referred them to a subgenus Actinometra in which the number of ambulacra! 

 grooves joining the excentric mouth is less than five, he used Alecto as a subgeneric 

 name for the species with five grooves, irrespective of the position of the mouth. Fifteen 

 species were definitely referred to this latter type in Muller's final memoir, and three 

 to Actinometra, the remaining seventeen being simply mentioned as Comatula, without 

 any further detail. 



More than a dozen years elapsed after the publication of Muller's systematic work 



1 Abhandl. d. k. Ahad. d. Wiss. Berlin, 1847 [1849], p. 245. 



2 Muller's diagram of the disk of this specimen is somewhat idealised, for it only represents forty arms disposed 

 in five groups of eight each ; whereas their number is really forty-nine, and the arrangement of the five primary 

 ambulacra at the peristome is by no means so symmetrical as shown in his diagram. 



