i58 



HARD WICKE'S SCIENCE- G OSSIP. 



how the amis of the Brittle-stars (Ophiuridae) and the 

 margins of the arms and body of the Cushion- stars 

 (Goniaster and Asterias) have been so regularly and 

 beautifully armed, the former even more effectually 

 than a mediaeval mail-clad knight. The two groups 

 so anciently separated, are easily recognised. Thus 

 the "five-fingers" and "sun-stars" (Solasters) so 

 abundant on our British coasts have the under 

 surfaces of their arms grooved. In and out of these 

 grooves we perceive rows of small, white, grub-like 

 objects which slowly wriggle to and fro if we turn 

 a star-fish on its back, and finally end by bending 

 over and attaching their tips to the rock by means 

 of suckers. Then by an united exertion they pull 

 over the star-fish to its proper position. A young 

 observer has not long to experiment on living star- 

 fishes before he finds that these grub-like objects 

 serve all the purposes of feet— that the star-fishes can 

 glide along even perpendicular surfaces by their 

 means. They are hundreds in number, but all are 

 fashioned alike, and the mechanism which renders 

 them locomotive organs is of the most wonderful 

 character. These feet are termed by naturalists 

 ambulacral, but we defer a detailed description of 

 them until we come to speak of the Sea-urchins. The 

 stomach of this kind of star-fish is continued up each 

 arm, and this fact naturally groups together genera 

 which may have a greater number of arms than five, 

 as the "sun-stars" (Solaster) which have twelve. 



In the "brittle-stars" (Ophiuridae), on the con- 

 trary, the stomach does not extend to the arms, 

 although the nervous branches of the ganglion sur- 

 rounding the mouth do. The "sun-stars" have only 

 two rows of suckers, whilst the "five-fingers" possess 

 four. In the "brittle-stars" we have the central 

 disc covered with jointed calcareous plates, and the 

 arms defended by four rows of the same. There are 

 no sucking feet, however, but the arms are employed 

 as organs of locomotion, in which they are aided, as 

 Mr. Fred. Kitton has shown, by short hooks which 

 take hold of the surface and thus obviate the 

 necessity of sucking-feet. Nature has usually more 

 than one way of meeting a difficulty, and this is a case 

 in point with the progression of the star-fishes. 



Many star-fishes are characteristically deep-sea 

 animals, and perhaps the Echinodermata, to which 

 both star-fishes and sea-urchins belong, range to and 

 continue over deep parts of the ocean-bed, more 

 than any other group of marine animals. Thus, 

 during the deep-sea dredgings of the " Challenger " 

 we find such genera as Opliiomiisium, Arc/iaster, &c, 

 dredged up, the latter from more than a mile and a 

 half depth of sea water. A large star-fish, called 

 Leptychaster, allied to our Luidia, was brought up off 

 Cape Maclear, Kerguelen's Island, in very deep water. 

 Another genus, Hymenaster, was found to be very 

 widely distributed over the sea-floor, and at depths 

 ranging from about half a mile to more than three 

 miles. Star-fishes and their allies, sea-urchins, are 



usually the commonest fossils of the Chalk formation, 

 which we know was an oceanic deposit formed under 

 very similar circumstances to the " globigerina ooze " 

 of the mid- Atlantic. Dr. Wallich showed, when sound- 

 ing in the "Bull Dog" for the first Atlantic cable, 

 that the ocean floor was occupied by star-fishes, for 

 these animals came up attached to the sounding-lead, 

 and this incident first broke people's faith in the old- 

 received notion that absence of light in the deep sea 

 rendered it a desert for all bottom animals except the 

 Protozoa. 



The Asteridce (represented by our common "five- 

 fingers "), and the Ophiuridae or " brittle-stars," as 

 we have said, are found in Cambrian rocks. We 

 have seen specimens better preserved in the fossil 

 state than dried recent specimens usually are in 

 museums. Sea-urchins also lived in the Palaeozoic 

 epoch, but they do not appear to have thriven well. 

 Only two genera are known, and these are represented 

 by but few species during periods long enough to form 

 strata thicker than all the Secondary deposits taken 

 together. But when we come to the Secondary period 

 we find the Sea-urchins gaining ground. By-and- 

 by, as in the Chalk formation, they are wonderfully 

 common, and of multitudinous shapes and types. But 

 by this time the Encrinites, which we have seen were 

 so plentiful on the floors of primaeval seas, had begun 

 to decline. Broadly, therefore, it may be stated that 

 the Sea-urchins begin to flourish just when the Encri- 

 nites commenced to decline. 



The fossil star-fishes are not as a rule abundant, 

 unless perhaps, we except a particular stratum in the 

 Middle Lias, where they are so plentiful that the 

 seam is called the " star-fish bed." At Leintwardine, 

 where the Lower Ludlow rocks crop up and are 

 quarried, we meet with both the kinds of fossil star- 

 fishes of which we have been speaking. Speaking of 

 Protester Miltoni (one of the ancient " brittle stars "), 

 Mr. Salter says it is "abundant, and of all sizes," 

 meaning, we suppose, in various stages of growth. 

 Few localities are better worth a geological pilgrimage 

 than this part of Shropshire. It is only six miles 

 from Ludlow, where the celebrated "Bone-bed" of 

 the upper Silurian rocks may be advantageously 

 studied. The Lower Ludlow rocks at Leintwardine 

 are not much quarried, for they are a kind of " mud- 

 stone," of little commercial value. Otherwise there 

 is no doubt the number of fossil star-fishes which would 

 be exhumed would be immense. Unfortunately, since 

 Mr. Salter's time, the quarry where the fossil star- 

 fishes were once so abundantly found has been either 

 worked out, or excavation has been discontinued. 

 Mr. Marston, of Ludlow, has a splendid series of these 

 fossils, among them Prolaster Marstoni. Shepherd's 

 Quarry, near Ludlow, is another good hunting-ground. 

 In some respects, one species, perhaps the most 

 beautiful of the entire group, named after Professor 

 Sedgwick (P. Sedgwickii), is allied to the "Feather- 

 stars" (or rather to one division of them called Euryale 



