ICHTHYOCRINIDAE 2J\ 



past century in England, Sweden and America, with the exception of some belonging to 

 /. piriformis from Dudley which is somewhat better represented than other species, and the 

 casts of /. corbis from Chicago. 



The form and proportions of the crown are not as serviceable characters in practice 

 as they should be, for the reason that in so many cases the specimen as found is distorted or 

 flattened by pressure, or only the lower part remains. The restorations I have made, based 

 on careful measurements of several specimens, show how erroneous an impression one may 

 gain from a flattened individual. Some range of variation is to be expected in this charac- 

 ter, but it is not so great in this genus as I had supposed. Measurements yielding certain 

 relative proportions show an average uniformity in the modifications of general form which 

 is of service in the separation of species. 



The sinuous outline of the transverse sutures, which has been relied upon in some cases 

 as a specific character, must be left out of consideration ; because as has already been shown 

 in regard to the group in general, while the sutures are more or less wavy on the exterior, 

 they are perfectly straight a short distance inward ; so that by a little weathering of the fossil 

 the sinuosity is effaced and the suture appears straight. The so-called " patelloid plates," of 

 which so much has been said in various descriptions, are only an incidental feature of this 

 structure, where the downward projecting lip or process at the middle of the proximal edge 

 of a plate has become cracked by contraction of the rays or by pressure in f ossilization, giving 

 the appearance of separate plates. 



The wavy sutures form a marked surface character in the genus, and they are probably 

 somewhat more pronounced in some species than others. I doubt if there is any species 

 entirely without them. In connection with this there is a peculiarity of the sutures in most 

 species — probably in all to a greater or less extent — which Conrad called " imbricated." The 

 upper margin of the plates is raised into a more or less abrupt step, which gives them the 

 appearance of overlapping the edge of the following plate, and it was this fish-scale-like 

 resemblance which suggested the generic name. 



The relative development of basals and inf rabasals seems to afford some tangible ground 

 for distinction ; and so also does the surface ornament. The latter character is often obscured 

 by wear or weathering, but by careful examination near suture lines, or in sunken and there- 

 fore better protected places, one may usually discover it if present. Two kinds of surface 

 are to be found in this and allied genera : One consists of a very fine network, representing 

 the surface growth of the stereom constituting the plates (PI. XXIV, fig. na), such as we 

 find on the outer skin of the Recent crinoids ; such a surface should be called smooth. In the 

 other the stereom itself is elevated into more or less well-defined granules or small nodes, 

 which by their confluence into straight or curved lines form distinct ridges ; or it is excavated 

 by pits and furrows, thus producing a rugosity wholly different from the simple meshes of 

 the first kind (PL XXXII, fig. n/). This rugosity varies somewhat in intensity, but it is 

 doubtful if the degree of such ornamentation is sufficiently constant for use as a specific 

 character ; however, the presence or absence of surface markings is apparently constant, and 

 furnishes the basis for one of the broadest groupings we have in this genus. • 



In the description of the species I make no attempt to give measurements, except to 

 indicate the maximum or average size, and certain relative proportions which often consti- 

 tute a useful guide and bring out the facts as to actual form better than ordinary descriptive 

 terms. This practice is especially useful in the treatment of this and allied genera, by 

 reason of the misleading appearance of the specimens due to flattening. In order to have 

 data for comparison I usually take the width at the level of the upper secundibrach, 

 the vertical height from the base to that level, and the diameter by calculation either from 

 the circumference measured on free specimens, or computed from the width of the secundi- 

 brach at that point. The measurement is taken at the upper margin or apex of the plate 



