4 6 



THE CYSTIDEA 



structure of stereom, absence of stem and of definite base of attachment, 

 absence of arms, absence of ambulacra, a single and independent gonopore 

 as in Holothurians. Ccdix, Rouault (1851-78 ; syn. Craterina, Barr. pars, 

 1887), Ordovician, France and Bohemia (Fig. IV.). The theca is a bowl 

 or vase of very thick plates, with an oral covering of very thin ones 

 rarely preserved. There is usually a marked hollow at the lower end, 



FICJ. VI. 



1, Cnlix bohe mica, from tlie side ; towards the base the pores are covered by a smooth epi- 

 dermis. 2, C'. excavata, the tegmen. Botli nat. size. (After Barrande.) 



but 6'. Sedgwicki, Renault's type- species, has a short, stem-like promi- 

 nence (St). The canals in the plates tend to definiteness of arrangement, 

 especially at the lower end, where they seem to radiate from the hollow. 

 The connection of the canals at their outer ends, to form pairs, is often 

 marked (Fig. V.). All these characters are exaggerations of some already 

 noted in Aristocystis. The tenuity of the upper surface, and its conse- 

 quent disappearance in most specimens, have 

 permitted the recognition of only one aperture, 

 which is pentagonal, and probably represents the 

 anal pyramid (Fig. VI. 2). Specimens with hydro- 

 phores palmtes have been referred to this genus, 

 but belong to (p. 73) Diploporita. Pilocystis, 

 Lapillocystis, and Acantlwcystis, Cambrian, and 

 BaculocystiSj Ordovician, Bohemia, all described 

 by Barrande, are probably referable to this order 

 if not to this family. Lodamlla, Kayser (1885), 

 Lowest Devonian, Germany, though called a 

 sponge, is very like Calix. Deutocystis, Barr. 

 (1887), Ordovician, Bohemia (Fig. VII.), is dis- 

 tinguished from Aristocystis by the greater irregu- 

 larity in size of the thecal plates (comparable to 

 the arrangement of plates in the carapace of some 



^_ , restored extinct edentates, Glyptodontidae), and by the 

 on the evidence of Barrande, absence of an independent gonopore, this having 

 Fig. 1 !!."' 8 ' Lettering " 8 in fused either with the anus or with the hydropore. 

 There are signs of fixation by the aboral end of 

 the theca (#), where the plates are larger and tend to lie in rows. The 



Fio. VII. 



