l86 SMITHSONIAN INSTITUTION 



Pycnosaccus patei n. sp. 



Plate XII, figs, i-p 



Specimens averaging large. Galyx somewhat similar to that of P. scrobicu- 

 latus, but slightly higher, less sharply angular, the side outline curved instead of 

 straight ; there are no pits or depressions at the junction of sutures ; the costae 

 are more delicate and usually lack the horizontal ridge connecting the radials. 

 There is a decided and constant difference in the form of the base, which instead 

 of being broad and truncate is narrow, and the lower part of the inf rabasal ring 

 is contracted into a neck projecting downward but little larger than the column; 

 on account of this narrow base the spread of the calyx to top of radials is far 

 greater than in the type species, being on an average in 10 specimens about 

 i to 4. A well-proportioned mature specimen with arms folded measures: 

 crown, 38 mm. high by 29 mm. wide at top of RR; base at IBB neck, 7 mm. 



IBB fairly high, erect, lower part forming a cylindrical rim. R facets nar- 

 rower than in P. scrobiculatus, the average width to that of R being 1 to 1.7; 

 they are somewhat elevated above the general margin of the radials, leaving 

 rather sloping shoulders, and usually having a slight projecting rim along the 

 entire margin of the radials, which perhaps takes the place of the transverse 

 ridge in the Swedish species. IBr 1 ; IIBr 3 or 4. Arms moderately strong, 

 usually somewhat angular at the back. Column relatively small, about one- fifth 

 the width of calyx at top of RR, and of less diameter than the inf rabasal rim; 

 composed of strong rounded columnals with smaller ones interposed somewhat 

 irregularly. 



This species is represented by a series of 15 specimens in fine preservation, collected for 

 me by Pate during his quarrying operations near Decaturville, Tennessee, in the summers of 

 1906 and 1907. They were deposited in a very fine-grained shaly clay favorable to the preser- 

 vation of structural details, but the fossils are all changed into flint of various colors. In 

 associating the name of Professor Pate with this notable species, I wish to record my appre- 

 ciation of one of the finest pieces of systematic and scientific collecting that has ever come 

 under my observation. 



There is no such instability in the number of primibrachs in this series as in those of 

 Gotland. In the whole series of specimens, all of which have the arms preserved, there is 

 not a single variation from the single axillary plate following the radials. One peculiar 

 feature in this form not very well shown by the figures is an asymmetry in the calyx of many 

 specimens by which the column facet is pointed slightly out of the vertical axis, somewhat as 

 is seen in Ichthyocrinus corbis. In this case the inclination seems mostly toward the posterior 

 side, that being a little shorter and less convex than the anterior. In such a strong calyx as 

 this such a distortion would not be due to gravity ; but I have no explanation for it. 



Types. Author's collection. 



Horizon and locality. Silurian, Niagaran Group, Brownsport limestone, Beech River 

 formation; near Decaturville, Decatur Co., Tennessee. Since these descriptions were pre- 

 pared a species has been discovered in the Laurel limestone at St. Paul, Indiana, closely 

 allied to this but much more delicate in size and sculpturing. 



