10 Br. F. A. Bather — Studies in Edrioasteroidea. 



be short spines, at fairly regular intervals of about *2 mm., and each 

 a little more than -1 mm. long (PI. II, Fig. 5). These spinules were, 

 one supposes, attached to the turret-plates by strands of stroma, and 

 it is the carbonized remains of the latter that form the black spots. 



Diagnoses of the genus and of the species will follow the 

 descriptions of the other species. 



EXPLANATION OF PLATE II. 



Pyrgocystis sardesoni. 

 Fig. 1. Specimen A. Oral face. The supposed anterior ray is uppermost ; 



the bunch of spines supposed to be over the anal opening is near 



the lower margin, slightly to the right ; above this on the right is 



exposed a part of the right anterior ray with tubercles, x 7-5 diam. 

 ,, 2. Specimen A. Oral face. This photograph was taken before the 



specimen had been prepared quite so much as shown in Fig. 1. 



x 3 diam. 

 ,, 3. Specimen C. Lower or distal end of turret, showing the large lumen. 



On the right the wall is bent inwards a little, x 3 diam. 

 ,, 4. Specimen A. The turret from the supposed posterior side, x 3 diam. 

 ,, 5. Specimen A. Part of the turret wall seen in Fig. 4, further enlarged 



to show the spinules. x 11 diam. 

 ,, 6. Specimen B. The turret seen partly from above, showing how the 



centre is filled with plates. Portions of the shelly matrix still 



adhere to the sides of the turret, which is attached to a small 



fragment of rock, x 3 diam. 

 Figures 2, 4, and 5 are from photographs taken and worked up by 

 Mr. Walter Moran. Figures 1, 3, and 6 are by the Author. 



B. Pyrgocystis g-rayae n.sp. (PI. Ill, Figs. 1, 2.) l 



Material, Locality, and Horizon. — Among the echinoderms collected 

 by Mrs. Robert Gray in the Starfish Bed of Thraive Glen, Girvan, 

 is one, numbered by me K 8, which in general structure closely 

 resembles Dr. Sardeson's fossil. The Starfish Bed lies near the 

 summit of the Ordovician, as proved by the work of many geologists 

 and palaeontologists, whose remarks were summarized in my memoir 

 on Caradocian Cystidea from Girvan (1913, Trans. R. Soc. Edin., 

 vol. xlix, No. 6, §§ 6-8), where also the relationships of the Cystid 

 fauna to those of other countries were discussed (§§ 559-568). Like all 

 the fossils from the Starfish Bed described in that memoir, the present 

 one is an imprint, and only one side is preserved. 



General Description. — The differences between this, for the present, 

 unique Girvan fossil and those from St. Paul lie mainly in the greater 

 elongation and tapering of the turret and the elevation of the oral 

 face into a high dome. 



Detailed Description. — The oral face is mounted on a kind of Cup 

 distinct from the stem or turret. This cup is formed apparently of 

 thin imbricating plates, serially homologous with those of the turret, 

 but higher and more closely united. At the top they are almost 

 square-cut. In radial position they seem to bear no definite relation 

 to either the rays of the oral face or the vertical rows of plates in the 

 turret. Although these plates overlap at the sides, they all appear to 



1 Plate III, containing the figures of Pyrgocystis grayae, will be given with 

 the second half of the paper in the February Number. 



