LECAXOCRINIDAE 189 



Pycnosaccus canadensis (Whiteaves) 



Arachnocrimts canadensis Whiteaves, Contrib. Canadian Palaeontology, I, pt. 3, 1891, p. 208, pi. 28, 



figs. 2, 20. 

 Pycnosaccus canadensis, Minchin fide Bather, Zoological Record, 1891, p. 82. 



A very small species from the Mackenzie River basin of the Arctic region, 

 in the strata which are said by Schuchert ( Paleogeography of North America, 

 p. 546), to be Middle Devonian. As stated by Bather in the Zoological Record 

 for 1 89 1 it belongs to this genus, but the specimen is insufficient for the deter- 

 mination of specific characters. It has small infrabasals. 



Type. Museum Geological Survey of Canada. 



Horizon and locality. Middle Devonian ; Hay River, Mackenzie River basin, Canada. 



(?) Pycnosaccus dubius n. sp. 



Plate XIII, figs, na, b 

 The peculiar crinoid figured under the above name was found in Decatur 

 County, Tennessee, associated with Pycnosaccus patei and Hormocrinus ten- 

 nesseensis. The size and general outline of the crushed crown are shown, but 

 unfortunately the plates are so displaced that it is impossible to ascertain their 

 arrangement above the radials. There are two small IBB visible as triangles 

 at the side ; very small BB, large RR — at least twice the size of BB— with two 

 IBr, about two-thirds as wide as the RR. Whether iBr are present is doubtful; 

 the form of the radial indicates the contrary, as there is a rather distinct curved 

 facet with short shoulders, apparently rounded as usual in this genus. Nor can 

 anything be ascertained about the anal side. There are no ridges or surface 

 markings of any kind. One arm, well rounded, is intact in the upper part. The 

 general shape and size of the confused mass of plates is about what we should 

 expect for an average specimen of this genus or of Hormocrinus. The outline, 

 figure 11b, shows the probable composition of the rays, and the relation of the 

 basal and inf rabasal plates. 



The greatest peculiarity of this crinoid is its column, which is preserved entire ; it is 

 quite long, very wide at the proximal end, and tapers from there gradually to the extremity 

 where it becomes very small, ending in a point and evidently not attached. From the calyx 

 down for two-fifths of its length it is composed of uniformly short, slightly rounded 

 columnals — the upper ones one-sixth as long as wide ; these continue without alternation or 

 change except that of decreasing width for the distance mentioned, where the diameter is 

 reduced by one-half ; here the columnals begin to lengthen and they increase rapidly from a 

 length equal to one-half their width until at the distal end they are- very elongate barrel- 

 shaped, seven times longer than wide. This stem might be a variant of that of Hormocrinus; 

 except in the remarkable taper it has some resemblance to that of the Carboniferous Mespil- 

 ocrinus. The species might be of the type of Mespilocrinus minus the radianal, forming 

 thus an intermediate step between that genus and Nipterocrinus. Until further discoveries its 

 actual generic position must remain in doubt. 



Type. Author's collection. 



Horizon and locality. Silurian, Brownsport limestone, Beech River formation ; Decatur 

 County, Tennessee. 



