126 SMITHSONIAN INSTITUTION 



form of a calyx composed of prominent basal and radial plates, and well differentiated from 

 the succeeding structures. In this respect it is in marked contrast with Ichthyocrinus and its 

 allies, in which the base and the radials are an immaterial part of the crown, whose expan- 

 sion is chiefly above their level. Therefore there is not the wedge-like widening of the rays 

 from an insignificant radial to larger and increasingly wide primibrachs so characteristic of 

 Ichthyocrinus; but their form is fixed by the width of the radials, to which they substantially 

 conform except in the posterior rays, where there is some widening of the brachials to form 

 an arch over the anal plate. Hence in a typical species the sides of the rays are approxi- 

 mately parallel ; but there are species somewhat intermediate in this respect in which the 

 radials are diminished and the primibrachs increase. The genus is remarkable for the occa- 

 sional occurrence of only one primibrach. The usual number is two, and there are few ex- 

 ceptions to this in the Silurian species ; but in Schultze's L. roemeri, from the Devonian, it 

 varies with the individual, one being more frequent than two. Secundibrachs vary from 

 three to four, some specimens of L. macropetalus having three in all rays, some four in all, 

 while others have both numbers with varying degrees of preponderance. Tertibrachs, which 

 are rarely seen in full except in the last-named species, vary from six to nine, with another 

 bifurcation above. 



In the condition of the radianal this genus is not so primitive as genera like Ichthyo- 

 crinus, in which that plate is in the position of the lower half of a compound radial, or the 

 inf erradial ; here it is oblique, resting upon the right shoulder of the posterior basal, and 

 therefore, not being in contact with the right anterior radial, its outline is necessarily quad- 

 rangular (frequently with slight curvature at the sides) instead of pentangular as in those 

 cases. In this condition it passes from the Silurian into the Devonian, where the radianal is 

 somewhat reduced in size; and it is succeeded in the Carboniferous by Mespilocrinus, in 

 which the radianal has entirely disappeared. 



The infrabasals typically are large and well-developed plates, standing erect and form- 

 ing a part of the calyx wall ; 1 in some species they are less prominent, but in none except 

 Lecanocrinns meniscus are they such insignificant plates hidden under the column as in 

 Ichthyocrinus. The three Devonian species show a departure from the family type of large 

 infrabasals, but in that horizon we may always expect to find variation and uncertainty of 

 characters in preexisting genera. The basals are very large, often forming half the calyx 

 up to the radial facets ; the posterior basal, by reason of its contact with the anal and radianal 

 plates, is of a very different shape from the others, its geometrical figure necessarily result- 

 ing from these connections ; it is not larger than the others, and does not rise to such a great 

 height as in Mespilocrinus. The anal plate, truncating the posterior basal and forming one 

 boundary of the radianal, is very large, often rising to the height of the first secundibrach ; 

 it completely fills the interradius, and suturally connects by definite sides and angles with 

 the plates of adjacent rays, which arch over it, and abut in line above its apex. The arcuate 

 sutures are not usually so prominent in this genus, being scarcely ever seen on the radials. 

 The calyx of Lecanocrinus is much more strongly constructed than that of Ichthyocrinus; 

 its walls in the lower part are thicker, and the base less liable to distortion. 



There is also a very distinct difference in the column from Ichthyocrinus. Instead of 

 having a turbinate enlargement of equally thin plates at the proximal end enveloping the in- 

 frabasals and sometimes a portion of the succeeding plates (PL XXXIII), it is here cylin- 

 drical, of much less diameter than the infrabasal ring; and the proximal columnals in some 

 cases begin at once to alternate in length, gradually increasing until the internodals disappear, 

 and the ossicles become uniformly longer and rounded on the sides. In some species there is 

 no visible alternation of short columnals, and in some the contrast is carried to an extreme. 



This genus has been confused with Anisocrinus by Angelin, who figured under it a speci- 

 men of that genus, and it was classed by him in the family Homalocrinidae, along witb 



1 Text-fig. 9, p. 117. 



