CARADOCIAN CYSTIDEA FROM GIRVAN. 387 



composed of the alternating dimeres or of ossicles into which these have broken (or 

 from which they have been formed). Traces of this alternation are still discernible 

 in the rino-s, which consequently pursue a distorted course round the stem. Whether 

 or no they form a spiral cannot be proved in the absence of counterparts, but com- 

 parison with other Cystids suggests that they are true rings. The latter view is 

 perhaps strengthened by the structure between the rings. This is not easily seen 

 owing to the coarse matrix, but there is some slight evidence that it is composed of 

 smaller plates. In every case there seems to be a broader band of small plates between 

 the theca and the proximal ring. 



§ 107. Comparison with Dendrocystis Sedgwichi. — The more definitely cordiform 

 shape of the theca and the greater dependence of the lobes may be due in part to 

 different conditions of preservation. For similar reasons the slightly greater relative 

 width in D. Sedgivicki may be deceptive. In absolute size D. Barrandei is only 

 two-thirds of D. Sedgivicki. 



The greater equality of the thecal plates, and the absence of any that are umbonate 

 and folded are distinct points of difference. Other differences in the thecal plates, as 

 of stoutness or definiteness of shape, are too slight to be readily recognised. 



The brachial appendage appears to be relatively narrower. 



The stem is about twice the height of the theca, whereas in D. Sedgivicki it is three 

 times the height. The median region does not show the intercalated plates common in 

 D. Sedgivicki ; and in the distal region the alternation of the dimeres is more perceptible. 



For comparison with D. scotica, see § 149, 



Dendrocystis Sedgwicki. 



(PI. I. figs. 5-9. Text-fig. 8.) 



1867. Cystidea Sedgwicki J. BABRANDMj^Syst.Silm. . . . delaBoheme," vol. 3, "Pteropodes," 



p. 179. 

 1887. Dendrocydites Sedgwicki J . Barrande, " Echinodermes . . . Extraits du Syst. Silur.," 



8vo, p. 223. Also " Syst. Silur. . . . de la Boheme," vol. 7, " Echinodermes, 



Cystidees," p. 145, pi. 26; pi. 27, ff. 2, 3, 4, 6-18 (caet. excl.). 

 See also the works referred to in § 39. 



§ 108. Diagnosis. — A Dendrocystis with thecal width about equal to thecal height ; 

 thecal lobes level with stem -attachment ; antibrachial shoulder rounded off without 

 projection; plates having greatest diameters from ca. "6 mm. to 4'1 mm., and large 

 plates often surrounded by small ones ; several in lower third of theca umbonate and 

 folded. Length of brachiole probably always less than thecal height ; width tapering 

 from 5 mm. [?as much as 8 mm.] to ca. '9 mm. Length of stem three times thecal 

 height ; distal region with dimeres faintly subalternate, forming slightly barrel-shaped 

 columnals ; median region expanding gradually, with dimeres alternating and pushed 

 apart by intercalated plates ; proximal region annulate, the rings composed of small 

 plates, and the interspaces filled with still smaller plates. 



§ 109. Locality. — Zahorzan and Trubin, Bohemia. 



