CARADOCIAN CYSTIDEA FROM GIRVAN. 



369 



havinw the vent lateral and adcolumnal, the intake lateral and a-columnal and connected 

 with a single skeletal process composed of four series of ossicles; with a stem proximally 

 widening and composed of small widened ossicles, distally subcylindrical, gently tapering, 

 and composed of elongate dimeres, and intermediately of transitional composition, 



8 34. Included Genera. — How far the above diagnosis excludes the Rhipidocystidae 

 I am unable to ascertain from the published account of that Family. If it does not 

 exclude them, then I should be inclined to reject the Family, and to place its single 

 genus in the Dendrocystidae. The sole really distinctive character of Rhipidocystis 

 (as diagnosed) is the outgrowth from the stem of flattened or, in the distal region, 

 sack-like, plated appendages. This, while admissible as diff"erentiating a genus, is 

 scarcely enough ground on which to establish a Family. 



§ 35. The genotype of Rhipidocystis is R. gigas Jaekel (1901, p. 672), said to be 

 from the Lower Ordovician " Vaginatenkalk bei Petersburg. Thecal plates ca. 2 cm. 



Fig. 3. 



Fig. 1. Fig. 2. 



Text-figs. 1-3. — Rhipidocystis. All the figures aie natural size. 



Fig. 1. — R. gigas. Specimen 1. Part of a theca from Nikolskoja. 



Fig. 2. — R. gigas. Specimen 2. Part of a theca from WeskinJe. The axial folds are slightly exaggerated. 



Fig. S.—R. baltica. Holotype. A stem-appendage. Reduced from Jakkel's original figure. 



large [presumably 2 cm, diameter], middle columnals ca. 1 cm. long, the sack-like 

 stem-bladders ca. 5 cm. long" {loc. cit.). Dr Jaekel kindly brought over some of the 

 original specimens for me to see while they were still in his keeping, but they yielded 

 no information as to the structure of the theca, beyond the facts that it was composed of 

 polygonal plates, irregular in shape and varying in diameter from about 25 mm, to 7 mm, 

 in the same individual, and that it was not conspicuously flattened. The plates are not 

 markedly swollen, and they have an irregularly granular surface, without other ornament 

 except for a faint suggestion of axial folds in specimen 2, The specimens consisted of: 



(1) a thecal fragment containing about 6 plates, from the Ordovician B 2 /3 of Nikolskoja 

 (text-fig. 1). This was labelled as a syntype, and belongs to the Petersburg Academy, 



(2) A thecal fragment of about 14 plates, from Weskinde ; horizon not stated (text- 

 fig. 2). This is at Greifswald University. (3) A thecal fragment containing a few 

 obscure but obviously large plates, of unknown locality. This is in the Volborth 

 collection at the Petersburg Academy, (4) A large slab from C 1, of Dubovicki near 

 Petersburg, bearing three root-bladders and the remains of one, perhaps two, appendages 



