May 20, 1880] 



NATURE 



55 



' Sarsens ' 



I SUPPOSE it is in the order of things that utility should be a 

 prime consideration, but still one cannot but regret the wholesale 

 destruction which is overtaking the picturesque stones which 

 have given its name to the "Valley of Grey Wethers," near 

 Marlborough. 



This destruction has been going on for some year-, as is wit- 

 nessed by the cottages in the neighbourhood built of "sarsen," 

 but has of late been vastly increased by the demand for this 

 strong stone for the bridges on the railway now making between 

 Swindon and Marlborough. Nearly all the large blocks have 

 indeed already disappeared. 



So far no attack has been made on the fine cromlech of the 

 " Devil's Den," which lies at the foot of the valley. It has had 

 a narrow escape before, for a weather-beaten shepherd told me 

 some years back that he "minded" how when he was a boy 

 the farmer there got all the horses and oxen and tackle he could 

 in the parish and laid on to the capstone, and " they drawed 'un 

 and drawed 'un, but il "uiarii't to be ttioved.". 



The geological interest in these rugged stones is consider- 

 able. They are found, more or less, all over the chalk range, 

 but always as scattered or isolated blocks. The temple at 

 Avebury was constructed of monoliths of this stone, so is most 

 part of Stonehenge. The cromlechs of "Kit's Cotty" .and 

 " Wayland Smith's Cave" are formed of it, and its cuiious 

 mode t)f weathering is well shown by the "blowing stone" 

 under Uffington Camp. There is hardly a vilkage amongst the 

 chalk hills in which a mass of this rugged stone may not be seen, 

 but nowhere is it found in anything like the abundance which 

 has characterised the "Valley of Grey Wethers." 



It is, I believe, the generally-accepted view that these 

 "sarsens" are the indurated remains of a tertiary stratum of 

 sand with which the chalk was once overlaid. Perhaps some of 

 your readers can inform me w here these stones can be seen in 

 their native sand. The c'rcumstance of the fracture of some of 

 the " grey wethers " near Marlborough disclosing imbedded in 

 them what look to me like chalk flints possibly points to an 

 earlier origin for them. A. G. Renshaw 



^ May 19 



AN ENTOMOSTRACON LIVING IN TREE- 

 TOPS 



IT is not to be wondered at that the moist and shady 

 hiding-places between the leaves of the Bromeliads, 

 filled as they are by food of various descriptions, should 

 be occupied by all sorts of animals, and that some of 

 these should have chosen them as their favourite abodes 

 and should have exclusively deposited their eggs in them. 

 And indeed, according to Fritz Miiller's friend, Frieden- 

 reich, almost ail the coleoptera peculiar to the Bromeliads 

 have been for the last thirty years found by him exclu- 

 sively in such places, and the same is probably true of 

 the larvae of very many species of insects, and for the tad- 

 poles of the tree-frogs, which undergo their meta- 

 morphoses therein. 



But for all this it is, as Fritz Miiller, writing from 

 Itajahy, November, 1879, says, a very astonishing thing 

 that there should be found living among the aquatic 

 animals in the tops of the woods a little crustacean whose 

 relations one is accustomed to find among the sea-weeds. 

 It is about one millimetre long, and is of the family of the 

 Cytheridae. 



Of the two cosmopolitan genera, each rich in species, 

 Cypris and Cythere, into which the untiring investigator 

 of the salt and fresh waters of Denmark, Otto Friedrich 

 Miiller, divided the bivalved Crustacea, those of the first 

 (Cypris) live almost entirely in fresh, and those of the 

 second (Cythere) almost entirely in salt, water. Only a 

 very few isolated exceptions to this rule have as yet come 

 to light, and in the Brazils Fritz Miiller only knows 

 Cythere as having marine species, while those of Cypris 

 are from fresh water ; and never would he have expected 

 to meet with, on the trees of his wood at Itajahy, an old 

 Baltic acquaintance which he erewhile had collected when 

 wading bare-footed with Max Schullze in Greiswalder 

 Bay. At the first glance he did not recognise the Cythere 



of the Bromeliads as a relation of its recent marine 

 cousins, because it differed a good deal in the shape of 

 its bivalved shell from all known species of Cythere, and 

 even from all known Entomostraca. These generally 

 possess laterally-compressed valves, which are broader 

 than they are long, and are commonly bean-shaped. In 

 the Bromeliad-lodger the length of the valves is a good 

 deal more than the breadth, and, in addition, the ventral 

 surface is flattened, and has a longitudinal furrow, 

 reminding one of a coffee-bean. In consequence of this, 

 when this new form is out of the water, instead of falling 

 on its side as the others would do, it falls upon its back, 

 or upon its ventral surface. This is probably an adapta- 

 tion to its place of abode. In the sea the species of 

 Cythere climb up on the narrow filaments of the algae ; 

 and in the Bromeliads they must move about on the flat 

 surfaces of adjacent leaves. 



While no recent entomostracon was known to Fritz 

 Miiller which this new form resembles, he was at once 

 reminded of a species {Elpe piiiguis) which occurs as one 

 of the oldest fossil Cytheridw, and which Barrande 

 described from the Silurian strata of Bohemia. This the 

 Bromeliad form very closely resembles, but it is just five 

 times as small. Fritz Mi^iller describes this new form as 

 Elpidiii))i bronteliarmu, for though it possesses no very 

 iTiarked peculiarities in its feet, still it does not fit into 

 even any of the genera into which the old genus Cythere 

 has been of late subdivided. 



ElJ'iilium BrmneUnrum.Yt. Muller. i , dorsal aspect ; 2, ventral aspect; 

 3, side view, right valve removed ; 4, anterior antenna ; 5. 6. posterior 

 antenn.iof maleandof female; 7, mandible ; 8, marilla ; 9, 10, 11. feet, 

 of ist, 2nd, and 3rd pairs ; 12, last body segments ; 13 and 14, egg and 

 young, from the parent valves; 15, Elpe tinguis, Earr. Magnified 

 I to 3 = 10 : I ; 4 to 12 = 71 : I ; and 13 and 14 = 36 : i. 



Everywhere that Fritz Muller has looked for this new 

 form, from the sea-side to some hundred kilometres into 

 the interior, he has found it common in the tree-frequenting 

 Bromeliads of the primasval woods. As it cannot, like 

 some other of the animals inhabiting such places, wander 

 from tree to tree, or even from one plant of Bromelia to 

 another, its distribution must be aftected by beetles 

 (Agabus, Laccophilus, Hisfer, &c.), or some other of the 

 Bromelia investing forms. The young Elpidia, when 

 they leave their mother, are only o'2 mill, long, and 

 doubtless they cling to some of the flying insects, and so 

 are transported. As, however, the colonisation of the 

 Bromeliads is thus seemingly entirely left to chance, it 



