494 Observations on the 



tially the same as those described by Messrs. De Koninck 

 and Le Hon, on page 61 of their excellent " Recherches 

 sur les Crinoides du Terraine Carbonifere de la Belgique," 

 which is thus translated : — " The genera Actinocrimis 

 and Platycrinus often show considerable traces of a mal- 

 ady which has the appearance of having been caused by 

 some parasitic animal. They are circular, shallow holes, 

 terminating in a rounded fosset, and distributed at haz- 

 ard over the plates of the body or the column. Around 

 the holes the substance of the plate seems to be raised or 

 tumid, in a manner circumscribed by a more or less prom- 

 inent ridge. This kind of excrescences may occasionally 

 attain a considerable development, assume the form of 

 globose appendages perforated at the centre, and deform 

 certain parts of the body or column." 



Several specimens of Cyathocrinus cornutus, Owen and 

 Shumard, have been found with one or more broad, shal- 

 low excavations in the substance of the plates, usually the 

 first radials near the junction of the arms. These cavities 

 are quite different from those previously mentioned, and 

 have the aspect of having been dissolved out, and do 

 not present the evidence of recuperative action that the 

 others do. 



Although the arrangement of the plates composing the 

 calyx of the crinoidea presents us in many cases with def- 

 inite generic characters, and though the formulas of these 

 plates have heretofore been almost exclusively used in 

 their classification, it has been long understood that in 

 some instances there were excellent generic characters pre- 

 sented in the mode of construction of the parts above the 

 calyx; yet these have not generally been available, either 

 for generic or specific distinctions, on account of the im- 

 perfect condition in which they were generally found. 



In the large collections lately made, it is not uncommon 



