i6 
SMITHSONIAN INSTITUTION 
Genotype. Gacaerinus inornatiis S. A. Miller. 
Distribution. Silurian to Devonian ; America. Not recognized in the foreign Silurian. 
The position and relations of this genus have been misunderstood. Bather placed it 
among the Flexibilia. Jaekel in his latest attempt at the systematic arrangement of the crinoids, 
Philogenie und System, 1918, does not fully agree with this reference, but in order to be on 
the safe side places it in each of his two most widely distinct grand divisions ; first under his 
subclass Cladocrinoidea, equivalent to the Camerata, in a family next to the Dimerocrinidae 
(p. 41), and then in his other subclass, Pentacrinoidea (p. 80), in a family Gazacrinidae under 
the suborder Calpiocrinites — an association of types about as incongruous as could possibly 
be imagined. 
As originally described, partly through errors of definition and partly through limita- 
tion of material, the essential characters of the genus were not fully disclosed, it being known 
only by two species from a single locality, specimens of which were rare and imperfect. Later 
acquisitions have furnished much new information, giving us now a series of seven or more 
species ranging through several formations of the Silurian in different localities and up into 
the Devonian. These have added greatly to our knowledge of structures unsuspected before. 
From them it now appears that the genus has ten heavy, biserial arms, directed upward 
and closely abutting. The tegmen is unlike that of others of the family, and is a distinct 
variation from that of the Camerata generally, being composed of a few large interambula- 
cral plates, surmounted by a set of triangular interlocking plates thought to be orals which 
vary in different species, being suturally closed or even anchylosed in some to form a solid 
pyramid with angular vertical ridges forming grooves into which the arms may fit. The 
various forms of this structure are well shown on plate 2, and from these it may be seen that 
there is a strong analogy between this tegmen and that of the Calyptocrinidae, as will appear 
by comparison with the figures of Euealyptoerinus erassus on plate 7, figs. 19, 20. This will 
furnish the desired line of connection with the Camerate type. See also Wachsmuth and 
Springer, N. A. Grin. Cam., 1897, pi. 81, figs. 12-15; and Hall, 28th Rep. New York St. Mus., 
1879, pi. 19, figs. I, 3, 4, 5. 
The interpretation of the pyramid of plates that we call orals is involved in considerable 
doubt. They are buried under closely fitting arms, which would affect the regularity of their 
development, and there is manifest in some species a strong tendency to fusion, by which the 
relation of the component plates may be greatly modified. 
The definition of the genus by Mr. Miller, and description of the type species, are erro- 
neous as to the composition of the base in the definite statement that it has “ no subradials ” — 
that is, that it is a monocyclic crinoid, which is a serious and fundamental error. This was 
due to loose observation, and the lack of careful preparation of the specimens to bring out 
the infrabasals at the bottom of the cavity, where they are plainly to be seen in more than a 
dozen of my specimens. Wachsmuth and Springer’s definition of Idiocrinus, based on the 
same species as Miller’s under a different name, specified the 5 small IBB at the bottom of 
the cavity, and the fact is shown by numerous examples of this and other species. It is also 
stated by Miller that the arms are composed of a single series of flattened plates, which was 
pure guess-work, and contrary to the fact as now known. 
Gazacrinus inornatus S. A. Miller 
Plate 2, figs, i-p 
Gazacrinus iiiornafiis Miller, i8th Rep. Indiana Dep. Geol., 1894 (adv. sheets, 1892, p. 49), p. 303, pi. Si 
figs. 9, 10, 15-17 . — Idiocrinus ctongatus Wachsmuth and Springer, Am. Geol., 10, 1892, p. 136; N. A. 
Grin. Cam., 1897, p. 203, pi. 18, figs. 8 a-c. 
Specimens small, average height to width at top of iBr 12 x ii mm. Calyx 
elongate conical. Base narrow with BB higher than wide, curving abruptly into 
