MORPHOLOGY 3 1 



As to the occurrence of the proximale generally he says on p. 212: 



All Recent and Mesozoic crinoids possess a proximale or strictly homologous structure, 

 typically single and attached permanently to the calyx, as in Millericrinus, Bourgueticrinus, 

 Phrynocrinus, Thiolliericrinus, and the comatulids ; but sometimes multiple, occurring all 

 together just under the calyx, as in Apiocrinus ; or at regular intervals throughout the column, 

 as in the pentacrinites ; or at frequent intervals in the proximal portion of the column and 

 becoming less common distally, as in Proisocrinus, Rhizocrinus, Bathycrinus, Monachocrinus, 

 and Democrinns. 



The second of these types of column, viz., with multiple proximales just 

 under the calyx, is comparable to that of those Flexibilia having a proximal 

 enlargement; while the stems of the remainder might fall substantially under 

 the fourth type — the nodal columnals being for the most part irregularly dis- 

 tributed. Every modern type of stem may be found in some Paleozoic crinoid, 

 but in none of the ancient groups had the stem characters become fixed and 

 correlated with other characters as in the later crinoids. 



Absence of a stem, and substitution therefor of a direct attachment by 

 the base as in some species of Edriocrinus or the remarkably similar Recent 

 Holopus, or of a free floating existence as in the Inadunate genus Agassizo- 

 crinus or the adult comatulids, is not known among the Flexibilia. 



b. Infrabasals and Basals 



All Flexibilia have a dicyclic base, with three unequal infrabasals, which 

 exceptionally disappear by atrophy, are fused into a solid plate in Niptero- 

 crinus, or appear as the primitive five in one species of Mespilocrinus. In this 

 character they are in contrast to the dicyclic Camerata and Inadunata, which 

 have five equal infrabasals, with exceptions in the latter. The small infra- 

 basal is radially situated, as the primitive segments of the other two would be 

 if they were bisected; but it would seem that the coalescence (if that is what 

 happened) of the two pairs, or the non-division of the two larger plates (if that 

 was the primitive condition as in some comatulids) was attended by conse- 

 quences which mark a rather wide difference between dicyclic crinoids with 

 five equal infrabasals and those with three unequal ones. Normally, as pointed 

 out by Wachsmuth and Springer (N. A. Crinoidea Camerata, pp. 58, 153), the 

 small infrabasal is in the right posterior position; but to this exceptions are 

 found in some species of Forbesiocrinus where this plate lies at the anterior 

 (PI. XXX, figs. $b, ja), or the left posterior {ibid., fig. 10), and rarely in one 

 or two other genera. 



In the Lecanocrinidae the infrabasals are usually prominent and erect, 

 forming a part of the calyx wall at the exterior. In the Ichthyocrinidae, how- 

 ever, they are buried under the column, lie almost flat, and take no part in the 

 formation of the exterior wall. Being thus without the function of calyx 

 plates, they exhibit in this family a marked tendency to atrophy. In two species 



