396 Prof. Bcyricli on the Base [Pelvis) 



form of the stem, sometimes by the five-leaved markings of 

 the articulating sm-faces well known in Pentacrinus, and 

 sometimes by the pentagonal or five-lobed form of the nutri- 

 tive canal that the directions determining the structure of the 

 stem are indicated. In Pentacrinus, the five smooth leaf-like 

 spaces of the articulating surfaces, the signification of which 

 was pointed out by Johannes Miiller, are directed from the 

 nutritive canal to tlie angles of the pentagon of the stem ; in 

 the middle of the sides originate the cirri, which owe their 

 position to a periodically recurrent division of the nutritive 

 canal in the five intervening directions. These two directions, 

 wliich are distinguishable in the same manner in other pedun- 

 culate forms, I will characterize as the jjenfaijetalous and 

 pentamerous directions of the stem ; they may occur either 

 together or alone. 



Stems like those of Pentacrinus, with pentapetalous angles 

 and pentamerous cirriferous sides, occur also in ancient Cri- 

 noids. Goldfuss has figured such stems from the Eifel, be- 

 longing to Poteriocrinus, under the name of Pentacrinus 

 priscus (Petrcf. Germ. Taf. 53. f. 7) ; and Murchison has given 

 figures of similar stems, from Silurian strata, without special 

 names (Silurian System, pi. 4. fig. 56). Pentagonal stems 

 without five-leaved markings on the articulating surfaces, in 

 which the pentamerous directions correspond with the angles 

 of the pentagon, occur only in palasozoic strata (Goldfuss, 

 Taf. 52. fig. 2, Cijathocrinus pentagonus). The directions of 

 the quinqueradiate nutritive canal always correspond with the 

 pentamerous directions of the stem, and therefore alternate 

 with the five leaves of the articulating surfaces when these 

 are present together with a five-lobed canal. 



In their position with reference to the base, the directions of 

 the stems of quinqueradiate structure are dissimilar. In Pen- 

 tacrinus the interradially placed segments of the monocyclic 

 base rest upon the five leaves of the pentagon of the stem ; 

 and the five pentamerous directions, or the five middles of the 

 sides of the pentagon, correspond with the radii. Upon this 

 peculiarity rests the assertion of Johannes J\Iuller (Ueber den 

 Ban des Pentacrinus, p. 16) that the base is a metamorpliosed 

 joint of the stem, and that its five pieces may be regarded 

 as divided parts of the five leaves of the stellate prism of 

 the stem-joints. This is the same thing as to say that 

 the stem is an appendage of the base or of the lower basal 

 circle, divisible in corresponding directions. That sucli a con- 

 ception is not in accordance with nature, appears from the beha- 

 viour of the dicyclic base in Encrinus, or still more distinctly 

 in the species of Poteriocrinus with a pentapetalous stem, such 



