CARADOCIAN CYSTIDEA FROM GIRVAN. 397 



5 '6 mm. Greatest diameter at right angles to the compression-plane, 3 '2 mm., or 

 exactly half the other diameter ; the corresponding diameter at the level joint-face is 

 2*3 mm. The other specimens differ in the greater absolute size of the dimeres, and in 

 the oreater alternation ; thus, in a dimere 10"5 mm. long, the angle that marks the level 

 to which the adjacent dimere rose is 6*4 mm. from the end (text-fig. 10). 



At the sides the dimeres slope to a sharp edge, which may bear a thin keel, usually 

 more pronounced towards the ends of the dimere (text-fig. 12). 



In connection with the alternation of the dimeres, the median suture follows an 

 extended zigzag of gentle curves. It is slightly depressed (text-fig. 10). 



The lumen, which has a diameter of "3 mm. in the largest specimen, follows a 

 straighter course (text-fig. 11). This is brought about, first, by the lumen being more 

 deeply sunk in each dimere ovei- the middle of its length ; secondly, by the slope of the 

 sutural faces, which in the neighbourhood of the angle slope towards the lumen, but 

 near the ends of the dimere slope away from it. This variation of slope tends to pro- 

 duce a slight locking of the dimere on one side between the two on the other side 

 against wliich it abuts. The sutural faces are smooth or slightly granular, and the 

 shorter of them may have a slight median tooth, which emphasises the locking. 



The joint-faces at the ends of the dimeres are flat and more coarsely granular ; the 

 granules are thrown into wavy lines with a tendency to radiate, thus producing a some- 

 w^hat vermicular appearance (text-fig. 12). 



Dendrocystis (?) paradoxica. 



(Text-fig. 13.) 



1859. Syringocrinus paradoxicus E. Billings, Canad. Org. Rem., dec. 4, p. 65, pi. 10, f. 14. 

 1881. Syringocrinus paradoxus [sic] Bill., "Parts of the ai'ms (?)," C. Wachsmuth and 



F. Springer, Proc. Acad. Nat. Sci. Philadelphia, 1881, p. 411. 

 1900. Syringocrinus paradoxus [sic] Bill., F. A. Bather, "Treatise on Zoology: Echino- 



derma," p. 48. 



§ 155. Diagnosis.— A Dendrocystis (?) in which the stem has a distal region 

 flattened, subcylindrical, with short dimeres regularly alternate distally and becoming 

 subalternate higher up ; median region expanding very gradually, with dimeres opposed 

 and (apparently) separated by intercalated plates ; proximal region composed of 

 numerous very thin wide plates ; no others observed. 



§ 156. Locality. — Beauport, near Quebec. 



§ 157. Horizon. — Trenton Limestone. From the locality one infers that the bed is 

 the Prasopora limestone at the top of the Kirkfield series (cf. § 406). 



§ 158. Material. — The specimen figured by Billings is of course the holotype, but 

 it appears that other more fragmentary specimens were found. 



§ 159. Remarks. — I have drawn up the diagnosis on precisely the same lines as those 

 of the other species ; but it is scarcely enough for the discrimination of the species. 

 The only point one can seize on is the regular alternation of the dimeres at the distal 



