112 Dr. F. A. Bather — Notes on Yunnan Cystidea. 



outer surface by a thin epistereom, so that on a well-preserved surface 

 they are at first invisible, and all that one sees is the finely-vermicular 

 ornament of the epistereom (E 7633). If, however, the surface be 

 wetted, it is usually possible to see the channels beneath, looking 

 much like the tunnels that a boring sponge or alga makes between 

 the layers of a mollusc shell (fig. 18). The manifestation of the 

 buried channels is generally increased by the fact that they are 

 injected with a fine mud, which has reached them through the pore- 

 canals from the interior of the test. It does not seem possible to 

 explain the appearances as due to anything other than a complete 

 coating of stereom. In thecas with diffuse channel-systems, the 

 outer surface, when well-preserved, is equable and smooth, except 

 for the fine ornament. 



In thecas with concentrated channel-systems, the outer surface 

 is raised into a little pustule over each system (E 7629, E. 7672, 

 E. 7673, see fig. 19). When slightly worn, the ends of the 

 channels are opened up and look like so many pores on the surface of 

 the pustule (fig. 20). Further wearing shows that in every case 

 there is only one diplopore to each pustule (fig. 21). Thus, Miller 

 writes of H. ornatus (1 878, p. 132): "Surface . . . pustulose . . . 

 The pores open upon the summit of the granules, and where the 

 granules are worn off, the plates show the pores, in pairs, passing 

 through to the interior." So also of JT. spletidens, Miller & Gurley 

 write (1894, p. 7) : " The whole body is pustulose and every pustule 

 is pierced by a pair of pores." 



These pustules with their appearance of many pores may be 

 compared with those vesicular multiperforate tubercles in Caryo- 

 crinus, of which so admirable an account was given by James Hall 

 (1852, Palseont. N.Y., vol. 2, p. 220). There a single pepper-box 

 pustule, as one may term it, may have as many as six outer openings, 

 but only one pore-canal leads to the inner surface of the thecal plate. 

 In older specimens the pustules of a single row enlarge till they 

 coalesce, "forming a vesicular ridge." 



The various modes of preservation and the differing amount of 

 weathering produce a number of diverse appearances in these two 

 plans of structure. Besides those already alluded to, one notes 

 that in the diffuse pattern weathering frequently affects the area 

 of the channel-system more than its boundary, so that the latter 

 stands up as a ridge ; possibly it is actually of denser stereom than 

 the channelled area. On the other hand, the injected material may 

 be more resistant than the stereom, and in this case the channels, 

 and especially the pore-canals, stand out while the surrounding tract 

 is weathered away. In some cases this eventually produces an 

 irregular pustulation (E 7630), which must not be confused with 

 the true surface-pustulation of the concentrated plan. It is plain 

 that the thecas were often lying for some time on the sea-floor, 

 and that their surface was then worn and overgrown in part by 

 bryozoans and other incrusting organisms. When fossilization took 

 place the open channels formed a key for the matrix, which 

 ultimately became firmly bound to them by secondary calcification. 

 In such cases the pattern shows up in sinuous ridges of pale 



