182 



THE GEOLOGIST. 



Fig. 2.— The same, of the natural size : the opposite side. 



Fig. 3. — The same : the base. 



Fig. 3«. — The same, magnified : the same view. 



Fig. 4. — The same, of the natural size : seen from above. 



Fig. 4a.— The same, magnified: seen from above. 



II. Genus Pisocrinus. De Koninch 



Formula.— Basal plates 5, united so as to form a triangle ; sub-radial plate unique, 

 placed at the side of the anal. 



Radial plates, known 1 + 5, of which two are large and soldered to the base, and 

 three are small and sub-triangular ; one of these last is intermediate between the 

 two large plates and welded to them ; the other two are welded partly to the anal 

 plate and partly to the large radial plates. 



The Calix of the species which belong to this genus is of very small size, and 

 in form globular or conoidal. The base is composed of five small pieces welded 

 together, of which three have a triangular form, whilst the two others are 

 quadrangular. The union of these five pieces forms a sub- equilateral triangle, as 

 shown in the diagram above. Each of its two sides supports one large radial plate, 

 of hexagonal shape ; these are welded together by one of their sides for the half 

 of their length, whilst the half-length on the opposite side is attached to a single 

 sub-radial plate placed on the third side of the base, and occupying thus the space 

 intermediate between the two great radial pieces, left free by them. This sub- 

 radial piece occupies the anal side of the calix — it is pentagonal. A radial plate 

 of triangular form, but much smaller than the two which are in contact with 

 the base, interposes in the form of a wedge between these latter ; two others of a 

 like triangular form alternating with the sub-radial plate. The stem ought to be 

 cj'lindrical, and of rather large dimensions in respect to the diminutive size of the 

 calix, judging from the impression it has left upon the base. 



Affinities and Differences. — 1 would have willingly referred the species 

 I am about to describe to the genus Triacrinus, established in 1839, 

 by the Count von Miiuster, if that palaeontologist did not expressly say 

 that the base of that genus is composed of three triangular pieces,^* for 



" This composition of the base makes me think that the genus Trichocrinus, 

 created subsequently by the learned anatomist of Berlin, J. Miiller (Monats- 

 bericht dor K. Akad. von Berlin, June, 1856, p. 354, and Phys. Abhandl. dor K. 



