116 , T. H. Witlters — Some Palceosoic Fossils 



mind the representatives of the recent genera Pyrgoma and Creusia, 

 and since the generic differences from Creusia are not readily apparent, 

 the term Palceocreusia is used tentatively to express the probability 

 that such differences will eventually be found. It may here be 

 pointed out that, while the recent and fossil forms included in 

 Pyrgoma have the shell in one piece, the sutures of the plates rarely 

 being seen, and then only those of the carina, in Creusia the four 

 compartments with their radii are quite distinctly seen. 



According to Clarke, "The specimen is attached to a colony of 

 Favosites hemisphcericus and has at some time been overgrown as far 

 as the aperture by the multiplication of the cell tubes. A portion of 

 the coral was subsequently removed by natural causes, exposing the 

 capitulum, but leaving the tubular basis completely enveloped. The 

 surface of the former still bears traces of the cell walls of the coral. 

 By removaL of a portion of the coral near the side of the specimen it 

 is found that the internal cavity is partially filled with soft decomposed 

 chert, the remainder of the cavity filling, the capitulum and the entire 

 coral being silicified. The internal plates, scutum and tergum, are not 

 preserved . . . The length of the tubular basis can be measured 

 through the aperture for 8 mm., but is probably somewhat 

 greater." 



The conspicuous furrow seen near the margin of the shell is 

 explained as probably indicating the line of contact of the wall of the 

 shell with that of the basis, but the furrow seems to me to be too far 

 removed from the margin for this to be the case. In recent forms the 

 wall of the basis is in direct contact with that of the shell at its 

 extreme marginal edge. In Clarke's figure the walls of the coral are 

 shown to extend on to the shell and converge towards the aperture. 

 -While this suggests that the figure is somewhat restored, it suggests 

 also that they are ribs of the shell, and not the walls of the coral at 

 all. Had these been the walls of Favosites one would have expected 

 to see them closed, and not left open, and to have seen traces of the 

 corallites hetween them. Moreover, seeing that the shell is so well 

 preserved, one would expect that the basis also would be preserved. 

 Despite the description of Clarke as to the supposed cavity for the 

 tubular basis, one wonders if this could not possibly be a mollusc of 

 the family Pissurellidse. That family extends back in time probably 

 to the Carboniferous, while tbe family, which Palceocreusia is con- 

 sidered to be a representative of, is not known earlier than the 

 Crag (Pliocene). Mr. Tom Iredale informs me that he has often seen 

 in the Indo-Pacific Oceans, members of the Fissurellidee attached to, 

 and even overgrown by coral. 



Since Pollicipes signatus, Aurivillius (Pig. 3), from bed e (= Lower 

 Ludlow) of the island of Gotland, in the opinion of the original 

 describer, shows a closer approach to the Balanidse than do any other 

 of the Lepadidee, it may more naturally be dealt with here. Only 

 a single specimen is known, and this certainly has the structure of 

 a sessile Cirripede, and bears little resemblance to the capitulum 

 of Pollicipes. Its structure is quite unlike that of any other known 

 form, and it is desirable to place it in a new genus, of which the 

 following may suffice for a provisional diagnosis : — 



