LECANOCRINIDAE 1 77 



other two species shade into the latter by rather close transitions, and all three may represent 

 merely the variations of a single prolific species flourishing abundantly under favorable 

 conditions. 



I have figured one of Hall's types and all of Ringueberg's, and besides these an excellent 

 selection of specimens showing all the variations in age and condition. Throughout them 

 all will be seen the same peculiar anal plate, suturally connected with adjacent plates, but with 

 its incipient longitudinal ridge continued by one or two similarly rounded small plates, mark- 

 ing the change toward the Taxocrinus plan. The sudden contraction of the arms just beyond 

 the third bifurcation is peculiar; after that they pass into finials of extraordinary thinness 

 (fig. 17). In further cleaning the type of L. nitidus I was much puzzled to find a structure 

 resembling pinnules between the slender arms ; but this finally proved to be a minute and per- 

 fect specimen of Homocriniis parvus entangled among the rays of the larger crinoid ; the 

 entire crown, including calyx and complete arms, is only about 11 mm. long (PI. IV, fig. 22). 

 As to surface ornament, this is so much dependent on the preservation and is so rarely seen 

 that it is useless here for specific characters ; as usually found the specimens are smooth. 



The narrow interbrachial spaces, less developed anal tube, and greater number of 

 secundibrachs, distinguish this species at a glance from A. bassleri. 



Types. One of Hall's L. ornatus, figure 1, is in the Cornell University Museum; the 

 other, figure 2, in the American Museum of Natural History, New York. Those of L. nitidus, 

 and the other specimens herein figured, are in the author's collection. 



Horizon and locality. Silurian, Niagaran, from the Homocrinus band in the upper part 

 of the lower third of the Rochester shales ; Lockport, New York. 



Asaphocrinus excavatus (Ringueberg) 

 Plate IV, figs. 23-29 



Lecanocrinus excavatus Ringueberg, Bull. Buffalo Soc. Nat. Hist., V, 1886, p. 11, pi. 1, fig. 7. — Springer, 

 Jour. Geology, XIV, 1906, p. 501. 



Similar to A. ornatus, but with wider interbrachial areas in which the peri- 

 some is often readily traced; the specimens are usually larger. The calyx is 

 fairly well differentiated in typical specimens, and is usually rather more turbi- 

 nate than rounded; height to width at RR, i to 1.4; the infrabasals are more 

 protuberant, forming a short cone. Height of B to R to IBr is as 4 : 3 : 2. 



In all these particulars except the last, the species represents an intermediate stage be- 

 tween A. ornatus and A. bassleri; in some specimens, such as Plate IV, figures 27, 28, 29, with 

 the interbrachial perisome distinctly shown in fairly wide areas, and the rather prominent 

 infrabasal cone, the facies is strikingly similar to that of the Tennessee form. The transition 

 from ornatus is very gradual, and with many intermediate specimens in the collection the dis- 

 tinction is uncertain. A maximum crown is 29 mm. high by 13 mm. wide; base 3 mm.; at 

 top of RR, 9 by 12 mm. ; spread of calyx from base, 1 to 4 mm. 



Types. In the author's collection. 



Horizon and locality. Silurian, Niagaran, from the Homocrinus band in the upper part 

 of the lower third of the Rochester shales ; Lockport, New York. 



