396 ' SMITHSONIAN INSTITUTION 



width, 21 mm. ; base at column facet, 4.5 mm. ; maximum specimen, 30 mm. high 

 by 24 mm. wide. 



IBB very low, barely visible. BB fairly large; post. B not greatly exceed- 

 ing the others and not encroaching on r. post. R. RR and IBr except the axil- 

 laries similar in size and form, less than twice as wide as long, without marked 

 taper; R somewhat the largest. IBr 3; IIBr usually 3, about uniform, the 

 divisions being at a wide angle; IIIBr 4 or 5, and 7 or 8. Anal tube rather 

 small, composed of plates somewhat longer than wide, the first one not mate- 

 rially encroaching on r. post. R. iBr numerous, extending into the second and 

 third axils, the distal margin of primary area concave and curving to meet 

 the brachials ; plates in all areas more or less depressed below level of brachials. 

 Column of the common type for the genus, enlarging at the calyx with very 

 thin columnals, and diminishing downward with the alternate columnals becom- 

 ing longer. 



The tegmen in this species extends high up between the IIIBr, the development of iBr 

 in this respect being more extensive than in any other species of similar size. In strictness 

 that should be considered the limit of the calyx, but to facilitate comparison I continue to 

 measure it at the arbitrary height of the top of the first axillary. The species is perhaps 

 nearest to the antecedent T. intermedins of the Kinderhook, and is in the same line of devel- 

 opment ; but the whole habitus is different, and with its widely divergent arms, low inter- 

 brachial areas and highly rounded rays, it is readily distinguished from that species. It is 

 not so easy to point out good characters to distinguish it from T. giddingei of the Warsaw 

 limestone, which will be considered under that species. The possession of a good series of 

 specimens enables me to show that in this Burlington species the 3 IBr of the typical Taxo- 

 crinus had become well established, for among 16 there is no departure from the rule. 

 Tabulation of the data from these also shows that with slight exceptions the 3 IIBr is the 

 normal character for this species, in contrast with T. juvenis of the Lower Burlington with 

 4 or 5 ; in other words it is essentially a shorter form. Among the 16 specimens in hand, 

 97 rami are exposed having IIBr as follows : with 2, 5 ; 3, 75 ; 4, 17 ; that is to say, 82 per cent 

 have 3 IIBr or less ; and in no specimen are there 4 in all the rays. It happens that a specimen 

 probably studied by Hall had 4 IIBr in some rays, and he so described the species. 



This species was first described by Hall, without figure, under Forbesiocrinus. Shumard 

 in his Catalogue of 1866, having first assumed that Onychocrinus was a synonym of that 

 genus and having therefore placed the O. ramulosus of Lyon and Casseday under Forbesio- 

 crinus, found that he had two species under the same name ; so he proposed F . subramulosus 

 for the present form. But as it is clear that neither belongs to the genus under which he 

 listed them, Shumard's proposed name must give way to the original. As above indicated, 

 the species is well represented, and was well known to all the early Burlington collectors as 

 the one described by Hall. Good specimens are in the Museum of Comparative Zoology, 

 Harvard, and other collections. 



Types. The species was never figured, and the record of Hall's original is lost. There 

 is a specimen in the Worthen collection, University of Illinois, among other types which were 

 studied by Hall, and this is probably the type, but there is no way of determining it. The 

 other specimens figured and used in the study are in the author's collection. 



Horizon and locality. Lower. Carboniferous, Upper Burlington limestone ; Burlington, 

 Iowa. 



