A. Smith Woodward — Greensand Ganoid Fkhes. 211 



bones, and even those of the cranial roof seem to be fused into a 

 continuous shield. The latter is elaborately ornamented with 

 closely-arranged, vermiculating rugae and tubercles. 



The smaller form of skull, known only by two specimens in the 

 Woodwardian Museum, is much depressed and scarcely exceeds 

 0-02 m. in width across the post-frontal region. The cranial roof 

 is likewise rugose, but exhibits very clearly the limits of the 

 parietal and frontal bones. The parietals are much elongated 

 antero-posteriorl}'^, united by a wavy suture and bordering the 

 hinder extremity of the frontals with their antero-external pro- 

 duction. The interdigitations of the mesial frontal suture are 

 especially deep and conspicuous. 



Family PACHYCORMID^. 



Genus Protosphyr^na, Leidy. 



Perhaps the commonest remains of ganoid fishes met with in the 

 Cambridge Greensand are portions of the rostrum of Frotosphyrcsna. 

 Not only are they abundant as specimens ; they are also of more 

 varied form than the corresponding fossils met with in any other 

 English Cretaceous horizon. In fact, if the rostrum alone suffices to 

 characterize the species of Frotosphyrcena, as is commonly assumed 

 and as seems probable, no less than five new types can be dis- 

 tinguished among these specimens. The typical species, P. ferox, 

 also occurs, and the characters of all of them may be briefly 

 summarized as follows : — 



1. Frotosphyrcena ferox, J. Leidy, Trans. Amer. Phil. Soc. vol. xi 

 (1857), p. 95. Woodcut, Fig. 3. 



Rostrum much elongated and attaining a length of about 0'3 m., 

 with a transverse diameter of 0-05 m. at its base where the vomerine 

 teeth are implanted ; circular in transverse section throughout its 

 whole length (Figs. 36, c), except within a short distance of the 

 vomerine teeth, where it becomes slightly flattened on the upper 

 part of its sides and the top (Fig. 3a) and passes into the gradually 

 widening flattened cranial roof; its. external surface ornamented 

 with reticulating rug^, of which the most prominent are longi- 

 tudinally directed. 



2. FrotospJiyrcena tenuirostris, sp. nov. Woodcut, Fig. 1. 

 Type. Rostrum : Woodwardian Museum, Cambridge. 



Rostrum much elongated and slender, somewhat flexed upwards 

 shortly in advance of the vomerine teeth, and attaining a length 

 of about 0-24 m., with a transverse diameter of 0027 m. at its 

 base where the vomerine teeth are implanted ; transverse section 

 (Figs, la-c) remarkably cyliudroidal throughout its length, slightly 

 depressed in its middle portion ; external surface marked by fine 

 longitudinal ridges. 



A slightly more attenuated form of rostrum from the Cenomanian 



