8 ME. P. H. CAEPENTER ON THE GENUS ACTINOMETEA. 



follows : — " Ce genre a la meme organisation que le precedent ; mais les especes ont les 

 bras ramifies au lieu de les avoir simplement fourchus." Agassiz consequently used 

 Comatula simply as equivalent to the Decacnemus of Linck, while his new genus Comaster 

 was Linck's Caput-Mediisce, or the Comatula multiradiata of Lamarck. Of the seven 

 other species constituted by the last-mentioned naturalist, only two, C. rotatoria and 

 C. fimbriata, have more than ten arms ; in both of these the number of arms is usually 

 twenty, though it may reach twenty-four, or possibly even more. Strictly speaking, 

 therefore, these two species, according to the above definition, should be referred to 

 Comaster, and not to Comatula. 



This character, the number of arms, upon which Agassiz founded a generic distinction, 

 is, in fact, extremely variable, and by no means of generic importance ; in fact, as 

 Goldfuss 1 remarked a little later, " Wollte man mit Agassiz die Theilung der Arme 

 als hinreichendes Gattungsmerkmal ansehen, so wiirde man folgerecht gezwungen sein 

 fast jede Art der Crinoideen als Gattung aufzustellen." 



Leach and Lamarck had already recognized this fact in uniting Linck's three genera 

 under a common name ; and it is not a little strange that Agassiz should have seen fit 

 to separate them again. His doing so, however, led to somewhat important consequences 

 from a systematic point of view. Turning to the fossil Comatula;, we find that Agassiz 

 erected the C. pinnata of Goldfuss into a new genus, Pterocoma, and grouped together 

 his other three species, C. tenella, C. pectinata, and C. filiformis, under the generic 

 name Saccoma ; while he expressed his belief thaf Solanocrinus was really related to 

 the Comatula;, and more especially to the problematical fossil described by Goldfuss 

 under the name of Glenotremites, which he rightly recognized as the centrodorsal piece 

 of a free-living Crinoid. 



In the year 1810 a new fossil Comatula was described by Hagenow 2 under the name 

 of Hertha mijstica. The specimen, consisting of the united first radials and hemispherical 

 centrodorsal piece, was somewhat worn ; but Hagenow was able to recognize the resem- 

 blance between it and the remains of Solanocrinus, and the corresponding parts of 

 Goldfuss's Comatula multiradiata, except that he was unable to find any trace of the 

 external basals which Goldfuss had described in both the above cases ; and though he 

 seems, and (as we now know) correctly, to have suspected "das Vorhandensein etwa 

 verdeckt-liegender Beckenglieder," he was, of course, unable to come to any satisfactory 

 conclusion upon the point. 



(§7) The year 18-10 is a noteworthy one in the history of our knowledge of the Crinoidea J 

 for it marked the appearance of the first of a series of classical memoirs by Johannes 

 Miiller, who laid the foundation of nearly all our knowledge of the zoology and morpho- 

 logy of the group : the first 3 of these was devoted to an anatomical account of the recent 

 and very rare genus Tentacrinus, together with many observations upon Comatula. 



1 "Beitr. z. rctret'actenkunde," N. Acta Acad. Leop.-Carol. Nat.-Cur. xix.A. p. 348. 



2 " Monogr. d. Riigen'schen Kreide-Versteinerungen, II. Abtheil. Eadiarien und Annulaten," Ncues Jahrb. Minc- 

 ralogie, 1840, p. G64. 



3 " Uebcr den Bau des Pentacrinus ccvput-Medusce," Abhandl. d. Berlin. Akad. 1S43 ; Abstract in Monatsb. der- 

 selben, 1840 ; also in Wiegmann's Archiv f. Xaturgescb. 1840, i. p. 307. 



