226 SMITHSONIAN INSTITUTION 



Genotype. Forbesiocrinus nobilis De Koninck and Le Hon. 

 Distribution. Lower Carboniferous, from base to Warsaw Group; Bel- 

 gium and the United States. 



No other genus of the Crinoidea Flexibilia has been involved in more confusion and 

 misunderstanding than Forbesiocrinus, both on morphological and nomenclatorial grounds — 

 so much in fact as to lead one eminent authority to suggest that the name be dropped alto- 

 gether. This has resulted largely from a misconception of its relations with Taxocrinus, 

 together with some uncertainty as to the exact limits of the genus as represented by the 

 specimens of its type species. It therefore seems advisable to give a somewhat full discus- 

 sion of the characters of the two genera, with the aid of information not possessed by previ- 

 ous authors ; and it is hoped that some of the difficulties which have troubled paleontologists 

 heretofore may be removed. In so doing I will take up the above mentioned causes of con- 

 fusion in inverse order. 



First, as to the definition and limits of the genus : It was founded by De Koninck and 

 Le Hon upon two specimens from the Lower Carboniferous of Belgium in the lowest stage, 

 the limestone of Tournai. These they erroneously identified with Taxocrinus nobilis of 

 Phillips from the Mountain limestone of Yorkshire, England (Research. Crin. Carb. Bel- 

 gique, 1854, p. 121, pi. 2, figs. 2a, b). They figured both specimens under the name Forbesio- 

 crimts nobilis, and gave a good generic diagram based upon them. They did not discover the 

 existence of the infrabasals, but described the genus as being devoid of them, and upon that 

 ground distinguished it and its ally, Taxocrinus, from Cyathocrinus and Poteriocrinus " with 

 which they had often been confounded." This may be disregarded as an error due to defi- 

 cient material, and to the unsuspected concealment of these plates under the column, which 

 caused them to pass unobserved in genera belonging to this group by many of the earlier 

 authors. Hall in 1858 (Geology of Iowa, vol. 1, pt. 2, p. 629), having several species to 

 describe which he thought referable to De Koninck and Le Hon's genus, discovered in them 

 three small plates below the so-called basals. He thereupon proposed a revision of the generic 

 formula so as to include those plates, which he called " basals," and the five others above them 

 " subradials," in the terminology of De Koninck and Le Hon. 



The generic formula given by the authors (loc. cit., p. 118) among other things stated: 

 " interradials 12 or 13 ; anals unknown." The latter clause is misleading; they only meant to 

 say that the total number of anals was unknown, for in their generic diagram they figure five 

 ranges of these plates ; and in the diagnosis of generic characters, after stating that all four 

 of the ranges of " pieces radiales " are joined to " pieces interradiales " to the number of 

 12 or 13 for each regular side, they add: " the number of pieces anales must be considerably 

 more." And they proceed further : " That which distinguishes the anal side from the others 

 is that the superior extremity of the corresponding basal piece is united to two small anal 

 pieces, and that it has, in consequence, two articular facets more than the other four basal 

 pieces." These statements are of the utmost importance in the discussion further on. 



The two type specimens are both imperfect. That of figure 20, in the Museum d'Histoire 

 Naturelle, Paris, shows the general character of the rays and their divisions, and the tuber- 

 cular surface ornamentation, but nothing whatever of the anal or interbrachial structures. 

 The other specimen, figure 26, is in the Musee Royal d'Histoire Naturelle at Brussels. It is 

 somewhat better preserved as to the parts wanting in the first, but it is in an unfavorable 

 condition for observing all these structures with accuracy. It is very much flattened along 

 the antero-posterior axis to a thickness of 15 mm., while the width is 75 mm. The authors 

 figured it from the flattened anterior side where the ray is much injured ; and no interbrachial 

 plates are visible on either side of this ray, but at the left of the right anterior ray may be 

 seen interbrachials to the height of at least four ranges. I have figured this interradial edge 

 of the flattened specimen (PI. XXII, fig. ic), and it shows the presence of some 8 or 10 plates 



