476 PR0CEEDIN08 OF THE NATIONAL MUSEUM. vol.46. 



material has always been available. Under such conditions the elim- 

 ination of Homocrinus parvus as type of the genus seems unjustified. 



An examination of several specimens of H. parvus, including the 

 types, convinced me that the species was a monocyclic Inadunate 

 and bore not the slightest relationship to the forms commonly referred 

 to the genus. In order completely to clear up the matter, it was 

 necessary to have a specimen showing all the plates of the cup. A 

 specimen was kindly placed at my disposal by Mr. Frank Springer, 

 and by the use of specially ground needles and working under a Zeiss 

 binocular the minute theca was finally freed from the matrix. Wlien 

 cleaned and examined in a cell of glycerin the specimen showed all 

 the plates clearly. From this specimen figures 1-4, plate 42, and the 

 analysis of the cup given as figure 8, were made. The outline figure 

 of a crown and portion of column given as figure 5, plate 42, is approx- 

 imately accurate — as nearly so, perhaps, as a pen-and-ink drawing 

 of this magnification may well be. Exact proportions and details of 

 structure are not to be expected, however. For such particulars and 

 for exact measurements, reference should be made to the text. From 

 these figures it will be seen that the crinoid is a monocyclic Inadunate 

 of a rather unusual type. 



A description of the species Homocrinus parvus, the only known 

 representative of the genus, may serve equally well as a description 

 of the genus. 



The form is minute, the crown of an individual of average size ^ 

 giving a length over all of but 12 mm. In this specimen the height 

 of the dorsal cup is 1.6 mm. Despite their small size the maturity of 

 these crinoids may not be questioned. The specimens show none of 

 the signs of immaturity, either in structure or preservation. Further- 

 more, the large number of Homocrinus parvus that have been found 

 are of essentially the same size, which in itself is strong evidence in 

 support of the assumption that we are dealing with adult forms. 

 Not only must one admit that this material consists of adult speci- 

 mens, but also that there is no chance of its representing dwarfed 

 individuals. The stratum in which Homocrinus is found indicates 

 normal conditions of deposition, while associated fossils show no dimi- 

 nution in size. 



The cup is fusiform, slender, and so closely affixed to the tapering 

 column that it is difficult on casual inspection to determine where 

 the theca ends and the column begins. A difference in the clearness 

 of the calcite indicates the line of demarcation with exactness, how- 

 ever. The calcite of the basals is notably more translucent than that 

 of the column. A dorsal cup 1.6 mm. in height has a breadth at the 

 arm bases of 0.95 mm. and a breadth at the junction with the column 

 of 0.65 mm. 



» The measurements given here and elsewhere of various portions of the crinoid are all taken from one 

 individual. 



