LECANOCRINIDAE l6l 



it takes on a quadrangular form and more oblique position, resembling that of Lecanocrinus. 

 In one species it is absent, and if we had more satisfactory material I should be disposed to 

 separate this form generically, as it also has a more nearly heterotomous arm than the others. 

 But having only a couple of imperfect specimens, neither of them preserving the base, and 

 in view of the fact that the radianal seems to be otherwise unstable, and that these specimens 

 have the other characteristics of the genus strongly marked, the better course seems to be to 

 leave it as a variant. 



The mode of arm branching, or rather the degree of it, is not quite constant. Ordinarily 

 it is a regular dichotomy, the arms dividing into nearly equal halves which are continuations 

 of the preceding branches in the same direction. But in some specimens the division becomes 

 more or less unequal — the smaller branch being toward the inside of the dichotom. This 

 diversity is observed between specimens of the type species ; and in the form last above men- 

 tioned, where the radianal is absent, the irregularity is so great as to be fairly called 

 heterotomy. 



This genus is one of a small group of Silurian genera hitherto supposed to be confined to 

 Gotland, Sweden, which have been vaguely associated in the books, but which on account 

 of the insufficiency and incorrectness of Angelin's figures have been much confused. The 

 others are Homalocrinus and Calpiocrinus, from both of which Anisocrinus differs in the 

 existence or position of the radianal, the larger basal development, and the absence of the 

 remarkable specialization of the infra-base which characterizes those genera. From Lecano- 

 crinus, with which it has been most often confused, and Clidochirus, it differs in having inter- 

 brachials all around instead of only at the anal side. 



Although Angelin recognized a new generic form in the specimens he had, his diagnosis 

 contained nothing from which its characters could be inferred, and his description of the type 

 species added no further information; so that from the definition alone the genus would be 

 indistinguishable. To make the matter worse, he referred the best specimen he had to 

 Lecanocrinus, without any reason whatever which did not equally apply to the other speci- 

 mens. It may be supposed that the quadrangular radianal in the smaller specimen (Icon. 

 Suec, pi. 19, fig. 4) suggested its reference to Lecanocrinus, of which the author gave a 

 diagnosis calling for " parabasalia sex " ; but why he included plate 19, figure 3, which has no 

 radianal at all, and did not refer all the others which have the odd plate to Lecanocrinus 

 instead of making a new genus for them, is difficult to see. In addition to this, his figures 

 of A. interradiatus (Icon. Suec, pi. 22, figs. 18, 18a) were incorrect in failing to show the 

 actual construction of the right posterior ray. So when Wachsmuth and Springer in the 

 Revision of the Palaeocrinoidea undertook to define the genus, the only character of essen- 

 tial importance which they could specify was the arrangement and size of the " interradial " 

 and anal plates ; — saying that the description would " probably have to be modified when 

 more species are discovered." We, however, referred Angelin's so-called Lecanocrinus to 

 this genus. 



Nevertheless the specimens themselves, with the addition of the two since found, show a 

 well-characterized generic form, with a radianal generally present ; and this enables us to 

 place the genus upon tenable ground as I pointed out in 1906.- This determination has been 

 confirmed by the discovery of two other species in America — both also referred by their 

 describers to Lecanocrinus. It is unfortunate that this interesting and well-marked genus 

 should be represented by such a poverty of material — there being only about a half dozen 

 good specimens known in all the species. The typical forms of it have a contour unlike that 

 of any other; the large interbrachials produce a prominent swelling of the calyx, above which 

 the rays contract into a compact bundle of parallel arms which is squarely truncate above by 

 their infolding. 



