S40 Dr. FiTTON on the Strata below the Chalk. [App, A. 



PLATE XV. a. 



Siphonia pyriformis. (Goldfuss, Petrefactenkunde, tab. vi. fig. 7.) This plate represents several 

 varieties in the form of this Siphonia, with some details of its structure ; from which it may be 

 inferred that the upper, enlarged part becomes broader in proportion, and more pear-shaped, 

 as it increases in size. But although this may be stated as a general rule, the exceptions are 

 numerous, and there seems to be as much variety in the form of the full-grown specimens of the 

 fossil, as in that of the fruit from which this species has been named. 



Figure 4, a specimen nearly entire, shows the root-shaped, lower, part of the stem, by which it 

 was fixed to the rock on which it grew. The condition of the fossil does not enable us to speak 

 decidedly as to the original state of the external surface in the living animal : we can perceive, 

 however, that beneath the surface was a system of large tubular canals, placed in a circle, with 

 some degree of regularity as to their distance from each other, and succeeded at intervals by 

 other concentric circles of similar tubes. These are shown in the vertical and horizontal sections 

 fig. 6. and 7., which had been very carefully ground down by the late Mr. Miller, for the pur- 

 pose of showing the structure, and in the broken and abraded specimens, fig. 4. and 5. Fig. 8. is 

 a specimen of a lower portion of the stem which belonged to the late Mr. Goodhall, F.G. S- 

 Its external surface having been removed, the tubes which form the lower part of the stem are 

 well displayed : and a similar observation may be applied to the head, fig. 5. 



In fig. 9. a head is represented, the greater part of which is embraced by a Serpula. From 

 this tube being at present nearly half immersed in the substance of the head, and from the 

 groove-like impression visible in some places, it would appear that after the Serpula had attached 

 itself, the head must have increased considerably in diameter ; still, however, preserving its 

 general form and proportions, where not covered by that tube. 



PLATE XVL 



Fig. 1. PoUicipes Icevis: from Blackdown, Devonshire. Supposed to be of the same species 

 as Plate XL fig. .5, found in the Gault near Folkstone. 



Fig. 2. Serpula fiUformis. The mode of grouping in this Serpula is remarkable. It consists 

 of smooth, round tubes, slightly curved, and aggregated into elongated, often branching masses. 

 The tubes are rather thick, nearly equal throughout their substance. This fossil may be the same 

 with that which Goldfuss calls S. socialis, (Petrefactenkunde, tab. Ixix. fig. 1 2.) ; but as he iden- 

 tifies the species from the oolite with that of the green-sand, I would retain his name for the 

 former only. The substance of this shell in our green-sand fossil is thinner, and the tube gene- 

 rally more curved, than in the aS'. socialis of the oolite. 



■ Fig. 3. Serpula Tuba. Simple, almost solitary tubes, of nearly uniform diameter throughout; 

 shell thin. 



• Fig. 4. Serpula Vermes. The tube gradually increases in size, and has a carina along its 

 upper surface. It is a larger, coarser species than Serpula carinella, (Min. Conch, t. 598. fig. 2.). 

 S. conformis of Goldfuss (Petrefact. tab. Ixvii. fig. 13.) is like it, but has subangular sides. 



Fig. 5. Panopcea ovalis. The regularly oval form shown by the lines of growth, distinguish 

 this from the species found either in the crag or recent : neither does the anterior side gape so 

 much as in any of them. It is moderately convex and smooth ; the beaks are nearest the anterior 

 side, which is closed ; the posterior extremity is rounded and gaping. 



Fig. 6. Ml/a IcEviuscula. So perfect is this cast in calcedony, that even the asperities of 

 the epidermis, such as occur in recent species, are preserved. The shell, which is nearly twice as 



