76 F. A. BATHER, CK1.\( »IDKA OF GOTLAM). 



The stem of Heterocrinus is divided by 5 longitudinal sutures interradially placed. 

 This structure has not hitherto been observed in the Calceocrinidse, but it may be seen 

 in the new species Calceocrinus pinnulatus, in which the stem is larger than in other 

 species. Here the diameter of the stem, in its proximal region, is b' mm., and there is 

 a pentagonal axial canal with a niean diameter of 1,75 mm.: from the angles of the canal 

 traces of sutures are given off, and these would no doubt have been, as is always the 

 ease, more pronounced in the distal region of the stem. The sutures appear to be inter- 

 radial, but are slightly shifted to the riglit; i. e., as seen from below, in the direction of 

 the clock-hand. This is doubtless connected with that torsion of the crown which is so 

 obvious in Castocrinus. It will no doubt be granted that these sutures are ancestral in 

 nature, l ) and that in them the Calceocrinidas present another point of connection with 

 Heterocrinus. 



Diagnostie characters of Species. The just discrimination of the species of this 

 family lins proved no less difficult than the establishment of genera, for somewhat similar 

 reasons. First, the homologies of the different parts being misapprehended, variations ot 

 slight value have been regarded as permanent specific characters. Secondly, the rarity oi 

 well-preserved specimens usually renders comparison of large series of forms impossible, 

 so that one is liable to magnify into species what are really nothing but extreme varieties 

 of the same species. Thirdly, the peculiar habitus of these animals, with the posterior 

 side so generally hidden, and with the main arms closely compressed and hiding the arni- 

 lets or pinnules, has prevented the examination of many characters which in other families 

 are rightly regarded as of considerable importance. Of these difticulties the second and 

 third are still prominent in the case of some of the Gotland forms, and have hardly been 

 overcome by days of labour and nights of thought. The first difficulty however need no 

 longer exist, if the views here put forward be finally adopted. 



In the genus Calceocrinus specific differentice are chiefly afforded by the relative 

 width and heiglit of the cup, by the hinge, by the degree of separation of the halves of 

 the left anterior radial, by the arms, and by the arrangement of plates in the anal area. 

 The three latter points are however directly affected by the evolution of the family, and, 

 in common with some other points, such as the exact position of the stem articulation, 

 the clearness of the sutures between radials or between basals, and the degree of nodosity 

 in the arms, they naturally show considerable variations ainong individnals of a single 

 species. Such variations are always more nunierous and appear of greater importance 

 when a family or genus is undergoing rapid evolution; whether they are the effect ot 

 instability produced by the initial and subsequent changes, or whether they are them- 

 selves, throiigh natural selection, the cause of those changes, is a biological problem of 

 which the solution is no less difficult than it is important. Here it is only necessary to 

 emphasize the fact that in such a family it is impossible to found species upon isolated 

 fragments. Any comparison of these Gotland species with those of the same age thal 

 have been described in North America is therefore almost impossible, for either the spe- 

 cimens or the descriptions or the figures of these latter have been so imperfecl that it 



l ) See Brit. Foss. Crin. V. Botryocrinus. Ann. Mag. Nat. I List., ser. tj, vol. VII, p. 408, May 1891. 



