FOSSIL CRINOIDS. 125 



7. A plate below the opening, between the radials and resting on the pos- 

 terior basal: Fig. 2. 



With such an admitted diversity among specimens in the typical locality, 

 the differences observed among the American species, even granting Hall's 

 doubtful anal plate (which would be the same as case 7 above), there can be no 

 generic distinction based upon this character; and the first impression would be 

 in favor of referring all these species to the European genus. But it will be 

 remembered that the arms of Gasterocoma are not known beyond the lowest 

 brachials, which Schultze says (loc. cii., p. 95) are high, with a round cross- 

 section; this agrees with a set of detached arms from the Eifel which I have 

 supposed to belong to this genus, and which are simple, composed of brachials 

 about as wide as long, wholly different from those of Aracknocrinus. 



That there may be important differences in arm structure among forms of 

 this group having substantially the same calyx, is further indicated by the 

 discovery in the New York Onondaga of another form of this peculiar type, 

 having a similar calyx and axial canal but a totally different arm structure, for 

 which I have proposed the name Schultzicrinus (PI. Ill, figs. 1-7). Instead 

 of the very heavy, many branching arms of Arachnocrinus, with short, deep 

 brachials, it has five simple arms, which are broad and shallow like those of 

 Synbathocrinus. The radial facets are directed upward, and fill almost the 

 entire distal face of the radial, which is not usually the case in Amchnocrinus 

 and Gasterocoma. The position of the radial facets in the latter two genera is 

 very similar, that of Gasterocoma seeming to represent a smaller arm. Except 

 for this small difference, which is not very well marked in the specimens, we 

 should not be able, from the caljTc alone, to say which of these two thoroughly 

 distinct American forms ought to be referred to Gasterocoma. Therefore, 

 until further discoveries, it seems best to let the two genera stand, and add a 

 third. 



Another form of somewhat similar habitus and with an undivided base, is 

 Myrtillocrinus, which also has the radials perforated by a dorsal canal; but it 

 lacks the laterally opening anus, and in fact it is unknown how the anus is 

 located, as none of the specimens show it. I have refigured the type and 

 another specimen of the American species, M. americanus of Hall, for comparison 

 with the other genera (PI. Ill, figs. 8a, b, 9). It has a very deep radial facet, 

 indicating that the arms, hitherto unknown, must have been round and heavy. 

 A specimen was figured by Miss E. Wood (Smithson. Misc. Coll., XLVII, 

 1904, PI. XVI, figs. 2, 2a) consisting of the calyx with some of the arms and 



