230 



HARDWICKE'S SCIENCE-GOSSIP. 



resembled loaf-sugar (caused by a layer of quartz 

 being underlaid with white opaque chalcedony), and, 

 while in most cases the quartz merely occupied the 

 outside edge of the space where a sponge had once 

 been embedded, sometimes casts of the exhalant 

 sponge pores were made in chalcedony overlaid with 

 quartz. These specimens show most conclusively 

 that the latter was introduced after the flint had been 

 deposited around the sponge. 



The different varieties of chalcedony were even 

 more numerous than those of quartz. Many flints 

 were coated internally with tiny mammillations, some 

 with large ones which, when split open, showed 

 layers of different degrees of opacity. The lovely 

 milkiness of some of the specimens, andjhe delicately 

 tinted translucency of others, make them the most 

 beautiful objects I have ever seen ; while a great 

 many flints exhibit the gradation from black, through 

 deep purple, to an almost transparent chalcedony in 

 a very instructive manner. Among the different 

 colours we obtained, one, a deep green, was most 

 remarkable ; purple, reddish, opaque white, and 

 colourless being the most common. 



We have been rather disappointed in the foramini- 

 fera. Either the chalk at Luton and thereabouts 

 contains a comparatively small proportion of complete 

 ones, or our mode of looking for them was defective — 

 most probably the latter. I have, however, succeeded 

 in getting complete specimens of globerigina, textu- 

 laria, and one or two other allied genera, from washed 

 chalk from Luton. 



We obtained some capital specimens of sponges 

 from Luton and adjacent places. Those interested 

 in these fossils could get a fine collection in this 

 district, as it is rather noted for them. Spicules of 

 all kinds may be washed out in almost any quantity. 

 One peculiar variety exhibits five rays in the direction 

 shown in Fig. 141 a, another as in Fig. 141 b belong- 

 ing apparently to the tetractinellidse. Inside a flint I 

 found, duplicated in a pale yellowish-brown chalce- 

 dony, a most exquisitely delicate cast, resembling in 

 colour and appearance an ordinary Turkey toilet 

 sponge. 



We obtained several fine specimens of Pharetro- 

 spongia Strahani, perhaps the most common species 

 of the calcispongire. In every case the sponge was 

 embedded in flint, the upper part only being exposed 

 on the surface, which presented to view, when cleaned, 

 a beautiful, angular, though somewhat confused, net- 

 work of calcareous threads. 



Among the other finds which came to our bag 

 were a good specimen of coscinopora, a hexactinellid 

 cup-shaped sponge with a peculiar perforated exterior, 

 the holes of which, filled with flint, project in knobs 

 from the outside surface of the internal cast of the 

 skeleton ; vcrruculina ; a very fine specimen of 

 plinthosella ; a large Guettardia stellata ; a branched 

 sponge, somewhat resembling, though in outward 

 form only, the common Dorydcrma ratnosum, of 



which we secured some very fair examples, and a 

 great many ventriculites and siphonias, a cross section 

 of one of which is shown in Fig. 142. 



The curious bydrocoralline Forospkcsra globidaris 

 can be here obtained in great numbers, and we found 

 many specimens. 



Among the Senonian corals, Parasmilia centralis is 

 certainly the most common, and we secured several 

 good examples. This coral has a very pretty little 

 skeleton of variable length ; our specimens are from 

 J to f inches long. In the illustration (Fig. 143) a 

 rough attempt has been made to show the edges of 

 the " costEC," or ribs, on the upper part of the 

 " theca," or external wall. These are very con- 

 spicuous in the better developed specimens. 



Of the crinoidea we obtained, at Luton, part of the 

 head and a few joints of the stem oi Boiirguticrmtis 

 ellip'tiais and some scattered body plates of the star- 

 fish Oreaster obtnstis. The latter are very often found 

 on the surface of the flints, which furnish a larger 

 number of fossils than the chalk itself. 



Sea-urchins abound in this neighbourhood, and if 

 very great care be exercised, Cidaris clavigera and C. 

 sceptrifcra may be found with the spines in situ. 

 We secured some perfect examples of spines and tests, 

 but did not find them together. We obtained one of 

 the five segments of the test of C. pernornata, a very 

 fine object, with its rows of pentagonal plates, each 

 canying a large primary tubercle situated on a smooth 

 base to allow the edge of the socket of the spine to 

 revolve freely, and forming a curious contrast to the 

 rest of the plate, which is plentifully bestudded with 

 tiny tubercles, decreasing in size as they near its 

 edge. C. pernornata has very long, thin, channelled 

 spines with tiny thorn-like processes on the edges of 

 the channels. We obtained many specimens of 

 Micraster corangimizim of all sizes, and generally in a 

 fine state of preservation. One small one shows, in a 

 strong light, that strange lustre along the crystalline 

 facets of the calcite composing it, which so puzzles 

 the collector the first time he sees it. 



We also bagged several specimens of Echinocoris 

 vulgaris {Anaiichytes ovata), a specimen of Galeritcs 

 albogalerus {Echiiiocojius coniciis), and another of G, 

 subrotimdus. Many of these echinoderms, that 

 evidently lay at the bottom of the Senonian Sea 

 some time before burial, are perfect museums to the 

 palaeontologist, furnishing him with serpulce, polyzoa, 

 under valves of crania;, etc. We secured from 

 Burham a specimen of that queer worm Tercbclla 

 Lcwesiaisis (Davies) formerly described by Dr. 

 Mantell as a fish, and named by Agassiz Dcrcetis 

 elongatiis ; and several specimens of serpula and 

 vermicularia, but they can only be referred to two 

 species. 



We obtained a goodly gathering of polyzoa, in- 

 cluding escharina, Rcticulipora obliqua, Marginaria, 

 Holostoma contingens, lunulites, etc., from the outer 

 surfaces of flints and echinoderms, and from the chalk 



