28 F. A. BATHER, CRINOIDEA OF GOTLAND. 



narrow, with vertical and usually parallel sides, but sometitnes slightly spear-shaped or 

 even petaloid. 



Description. 



Dorsal cup varies greatly in shape, so inuch so indeed tbat one is tempted to make 

 more than one species: tlierc would however be so many connecting links that no diagnoses 

 would be possible. Similar variations in form are seen in most common and widelv distri- 

 buted species; thus, Eugenia crinus caryophyUatus has a series of shapes curiously parallel 

 to those of P. pilula, and Apiocrinus elegans Defr. (A. Parkinsoni auett.) varies in a very 

 similar manner. Many other variations in struetnre, e. g. the shape of the basals, are 

 direct consequences of the shape of the cup; while other variations, e. g. the shape of the 

 radial processes and the articulation of the stem, appcar indiscriminatelv in cups of different 

 shapes. I have therefore not even ventured to propose detinite varictal names; but shall 

 simply distinguish the shapes as conieal (Pl. I, tigs. 2, 6), ovoid (Iconogr. Tab. IV, f. 4, 

 4 a — b) and globose (Pl. I, tigs. 4, 5). The conieal form proper has straight sides and is 

 abrnptly trnncated above and below: the ovoid form is elongate owing to the greater 

 length of the large radials and the radianal, and curves inward gently above and below; 

 the specimens of this form are mostly very small: the globose form is lower in propor- 

 tion and gently rounded. The conieal form is the most common in Gotland; it is however 

 also found in England, and on such a specimen de Koninck founded his P. ornatns; 

 ainong American species its analogue is P. piriformis* A form between conieal and ovoid 

 is perhaps the most common in England: it is also found in Gotland (Pl. I, tigs. 3, 7), 

 especially in bed f; the type specimen of P. flagellifer (Pl. I, tig. 1) has a cup of this 

 shape; in America it appears to be represented by P. Benedicti. The true ovoid form is 

 rare in Gotland, and unknown in England, it has as yet oply been found in bed c: this 

 form if a ny should be distinguished as a variety or even species, but only 5 cups are 

 known and it may well be merely a, young stage. The globose form is very rare in Got- 

 land, but is common in England; such a form was de Koninck S type-specimen: in America 

 P. globosus and P. gemmiformis are of this shape. 



The following measurements show the considerable variation in size and proportions: 



Height 18 6 5.5 4 3.5 3 2.8 2 mm. 



Width I 8.5 6.5 6.5 5.5 4 4.5 3 2.5 min. 



The plates have generally an equal curvature, as in the conieal form (Pl. I, tig. 2); 

 but they are often slightly swollen, as in the ovoido-conical forms (Pl. I, tigs. 3, 7), and this 

 is usually the case with the English specimens; this swelling, being naturally more visible 

 in the three larger plates (viz., ant. R, 1. post. R and R'), produces a trilobate section (Pl. I, 

 tig. 7), and this, thongh not shown in Angelix's Tab. IV, f. 4 b, is especially marked in 

 the ovoid form, where these three plates have a greater rclative size. 



The surface of the plates is usually smooth as in all other species of the genus; 

 sometimes, however, a rough surface has been produced by weathering or other ex- 

 ternal causes, and of this nature was the ornament described by de Koninck in 

 P. ornatns. 





