4 



BRITISH FOSSILS. 



Explanation of Plate V. 

 Eigs. 1. 2. 3. and 4. Represent various views of the more tumid variety. 

 Mg. 5. Is a profile of the depressed form. 



Eig. 6. Ambulacral and interambulacral plates from the poster©- lateral segment. 

 Fig. 7. Arrangement of the pores in the ambulacral avenues and structure of the 

 apical disk. 



Figs. 8. 9. and 10. Illustrations of the dispositions of the pores in the anteal am- 

 bulacrum. 



Figs. 11. and 12. Primary tubercles and granules, magnified. 



Note on another British species of Hemipneustes. 



In lists of British fossils from the Lower Greensand a " Spatangus complanatus " is 

 often mentioned, and referred to as the Holaster or Toxaster complanatus of the Neocomien 

 of the Continent, a species upon which much stress has been laid by those geologists who 

 have described foreign localities. In Mr. Morris's coXdlogviQ iha Holaster complanatus is 

 made synonymous with the Spatangus retusus of Lamarck and Goldfuss, and the Spatangus 

 argillaceus of Phillips, which last-named fossil, judging from the figure given in the 

 " Geology of Yorkshire," was an Ananchjtes of the subgenus Holaster. The Upper Green- 

 sand of Wilts, the Gault of Speeton and Folkestone, and the Lower Greensand of Kent 

 and Hants have been enumerated as formations in which the supposed " Holaster com- 

 planatus " is found. In Dr. Mantell's jMedals of Creation (p. 355. lign. 84.) there is indeed 

 a figure of " Spatangus complanatus. Chalk Marl, Hamsey," which, being evidently a 

 representation of the true species of that name, might seem to imply not only that it is 

 really British, but also that in England it is found in a very different geological position 

 tlian on the Continent. But a comparison of the figures in question with those in Plate 2. 

 of the " Echinodermes Suisses " shows that they are copies or tracings of the excellent 

 representations of Neocomien, i.e. Lower Greensand examples, given by Agassiz in that 

 valuable v/ork. Probably Holaster suhglobosus was the species intended by Dr. Mantell, 

 and really found by him in the Chalk Marl of Hamsey. The specimens which have been 

 mistaken for Toxaster complanatus in the Wiltshire Greensand were possibly my Hemi- 

 pneustes Greenovii; those that I have seen so called from the Gault belong to more than 

 one species of Hemiaster, and that from the Speeton clay was either a Holaster or a 

 Cardiaster crushed. I have also seen examples of Cat'diaster Benstedi marked Spatangus 

 complanatus or S. retusus. 



I can find no evidence whatsoever of the occurrence of the true Toxaster (i.e. Hemi- 

 pneustes, as now redefined) complanatus in British strata. Very distinct sea-urchins, 

 members of no fewer than four different genera, have been intended by that name in 

 British lists. 



One of these, a Lower Greensand species referred to by Dr. Fitton, is really a Hemi- 

 pneustes of the section Toxaster. It differs however specifically from any known species, 

 and I have named it Hemipneustes (Toxaster) Fittoni. 



It has t?ie test tumid, ovate, depressed above, rounded inferiorly, with a shallow anteal 

 sulcus. The lateral ambulacra are partially petaloid, and in that portion of their length 

 lodged in very slight depressions. The avenues of pores in the odd ambulacrum are placed 

 rather widely apart. Those of the antero -lateral ambulacra are slightly sinuous, and the 

 outer ones are very slightly broader than the inner. There are about 36 pairs of pores in 

 the petaloid part of each rovf. The postero-lateral ambulacra are much shorter and more 

 symmetrical, and have about 1 6 pairs of pores in their petaloid parts of each row. The 

 tubercles on the plates are small, pretty equal, and scattered profusely. 



The dimensions of a moderately large specimen are one inch and ^ths in length, one 

 inch and -j^ths in breadth, and ten-twelfths of an inch in height. 



In the Museum of Practical Geology is a specimen from Horseledge Point,; near 

 Shanklin, Isle of Wight, presented by Dr. Fitton, and another from Hythe, presented by 

 Mr. H. B. Mackeson ; both froni the Lower Greensand. 



October, 1852. EowAPtD Foebes. 



