340 SMITHSONIAN INSTITUTION 



Scotland, which proved to be of the greatest interest. Among them are no less than twenty 

 specimens of this species, and they confirm in a most satisfactory way the validity of the 

 characters upon which the genus was founded. The doubling of the interbrachial series in 

 the regular areas, -contrasted with the single series in the anal area, is constant throughout 

 except in a single interradius. 



There is a peculiar tendency to infirmity at the anal side, where the anal x frequently 

 appears sunken or as if gone altogether, but with the succeeding plates in the series perfectly 

 solid and normal. This condition is seen in figures ga, b, of Plate XL, and exists also in the 

 original of figures na, b; 8 out of 12 of the new specimens preserving these parts show it in 

 the same way, while four appear to have all plates of the anal series intact. Such a pre- 

 ponderance of specimens with the anal side so affected would seem to indicate a morphological 

 change having some relation to the diminished size of that interradius characteristic of the 

 genus. 



This malformation of the anal area is not quite characteristically shown on Plate XL, 

 figures ga, b, where it appears as if the missing plates might have been accidentally broken out. 

 In all the other specimens the margin of the sunken area is distinctly rounded, showing that 

 for some unknown cause it had grown that way. Indeed it somewhat resembles the lower part 

 of the posterior area in Taxocrinus, but there is no sign of any tube, and some plates firmly 

 united to the rays at both sides are always found in the upper part. As this is the latest known 

 genus of the suborder with the strong anal side, we may have here a case of degeneration 

 tending toward a return to the primitive weak anal side, analogous to that of Synerocrinus. 



It has been suggested that these depressions may be caused by parasitic shells, like those 

 made by Eiilima upon the calyx of Ptilocrinus, but they are scarcely regular enough in shape 

 for that. 



The tendency to resorption of the infrabasals is also remarkably shown by the new 

 material — these plates being wholly resorbed in three specimens, partially so in nine ; while in 

 four others they remain intact. In each case where complete resorption has occurred, the 

 axial canal is nearly or quite radial. 



The above-mentioned fossils in Mr. Wright's collection are associated with a remarkable 

 and hitherto undescribed crinoidal fauna, of which a very clear account, with photographic 

 figures but without specific descriptions, is given in his papers (Trans. Edinburgh Geol. Soc, 

 vol. 10, pt. 1, 1912; pt. 2, 1914). The fauna occurs in the Hurlet formation, a series of alter- 

 nating sandstones, shales and limestones covering upward of one thousand square miles in 

 Scotland ; it represents the top of the British Lower Carboniferous limestone series passing 

 gradually into Coal Measures. Among the other genera comprising this fauna are Hydre- 

 ionocrinus, Cromyocrinus, Zeacrinus of the true Z. wortheni type, and Synerocrinus. This 

 assemblage of crinoid forms at once suggests the equivalency of this horizon with that of the 

 Russian Bergkalk near Moscow. It is also directly comparable with the Kaskaskia of the 

 American Lower Carboniferous, with which its stratigraphic position preceding the Coal 

 Measures precisely agrees. 



Types. British Museum of Natural History, London, Nos. E7422, E640. The original 

 of figures 11a, b, is in the collection of Mr. E. Dunlop, of Baillieston, Scotland, now in the 

 Carnegie Trust Museum, Dunfermline. 



Horizon and locality. Upper part of Lower Carboniferous, comparable to the Bergkalk 

 formation near Moscow, Russia, and to the Kaskaskia of America. Invertiel, Roscobie, 

 Lesmahagow, and Rutherglen, Scotland. 



