App^ A'.] Dr. PiTTON on the Strata below the Chalk. 337 



which has two acute keels ; the lip has a long forked projection arising from the upper keel ; 

 the beak is long arid subulate ; the whole surface striated. 



Fig. 20. AmmO'hites'i circularis. Aperture circular; whorls just touching each other: nearly 

 close, acute, circular; sometimes forked ridges cover the surface. This specimen may, perhaps, 

 be a portion of an Hamites or Scaphites ? 



Fig. 21. Ammonites symmetricus. Aperture nearly square; ribs blunt, slightly tumid as they 

 approach the hollow in which the rounded keel is immersed, and though not equal in length, 

 elegantly uniform in their elevation ; tlie sides of the whorls flattened. The specimen here fi- 

 gured, though a fragment only, differs from every Ammonite known to me. 



Fig. 22. Ammonites crenatus. Sides flattened; the inner whorls much exposed, their margins 

 nearly smooth and rounded, those of the outer whorls crenated on each side of a narrow concave 

 space over the siphuncle. Distinguished from A. splendens by the more exposed inner whorls. 



Fig. 23. Ammonites cristatus. (De Luc, in Brongniart, Env. de Paris, pi. vii. 10.) Some of the 

 ribs being acute and much more elevated than others, form the distinguishing character of this 

 species. I believe A. cristatus and A. suhcristatus of De Luc to be varieties of the same species : 

 I have seen both from Folkstone : the specimen before us belongs rather to the latter variety. 



PLATE Xn. 



Figs. 1, 2. Hamites rotundus. (Min. Conch, tab. Ixi. fig. 2, 3.) The peculiar structure of the 

 inner extremity in this species, is indicated, rather than distinctly seen, in these figures ; which 

 have been engraved from drawings by the Rev. G. E. Smith, taken from specimens collected by 

 Lord Greenock, near Copt Point in Kent. Mr. Smith observes, in a note sent with the drawings, 

 that the termination in a minute whorl, (imperfectly seen in the figures,) had been 

 traced distinctly in more than one specimen ; which proved that the coils of the spiral 

 were nearly parallel to the straight part of the stem, and the axis at right angles to 

 it. The spiral appears to have been open, as in many recent Serpulae ; so that its 

 perfect preservation in the fossil could scarcely have been expected : and this would 

 account for the defective state in which the Hamite is commonly found. Mr. Smith adds that the 

 spiral portion appeared invariably to have been decayed, as if it had been filled up with soft 

 matter, as in the case of Magilus. The figures show the remains of the spiral, in two different 

 specimens; but in botli much broken and displaced. The spiral part is round, with contiguous 

 annular ribs, also round and regular. 



Fig. 3. Hamites attenuatus. (Min. Conch, t. ixi. fig. 4. and 5.) Both ends of this species, when 

 complete, are similarly bent or folded in, not spirally, but so that the segments become parallel 

 to each other. The larger parts are rather compressed, the smaller cylindrical ; the ribs are 

 annular and rounded. 



Fig. 4. Hamites spiniger. The general form of this species is like that of Scaphites Yvanii, 

 (Bull, de la Soc. Geol. de France, vol. ii. p. 355, pi. ii.) ; one portion being a flat volute, like an 

 Ammonite, but with unconnected whorls ; the other bent into the characteristic form of a Hamites : 

 the sides are flattened. The spines form one of the chief specific cliaracters : there are three 

 rows of them on each side, placed upon the larger ribs on the involute part of the shell ; they are 

 gradually lost upon the other parts. 



PLATE Xin. 



Fig. 1. Echinus'', arenosus. The underside is imperfect, and the genus therefore doubtful. 

 Fig. 2. Panopcea rotundata. Only a cast, which is nearly smooth. The ridge separating the 

 posterior area, which is small, is strongly marked, and projects on the margin. 



3x3 



