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XXI. On the Ecliinoidea of the ‘ Porcupine ’ Peep-sea Dredging-Expeditions. 
By Professor Wyyille Thomson, LL.D ., D.Sc., F.B.S. 
Abstract received June 15, — Read June 20, 1872. 
Section II. received April 4, 1873. Sections I. & III. received April 9, 1874. 
I. 
Received April 9, 1874. 
The deep-sea dredging-cruises of H.M. Ships ‘ Lightning ’ and ‘ Porcupine ’ during the 
summers of 1868, 1869, and 1870, in the North Atlantic, were comprehended within a 
belt 1500 miles in length by from 100 to 150 miles in width, extending from the Faeroe 
Islands along the northern and western coasts of Scotland and Ireland and the coasts of 
Portugal and Spain to the Strait of Gibraltar. In this area fifty-seven successful hauls 
of the dredge were made during the three summers in water exceeding 500 fathoms in 
depth, sixteen beyond 1000 fathoms, and two beyond 2000 fathoms. 
Even at the latter extreme depths Echinodermata appeared to be abundant. At 2435 
and at 2090 fathoms all the Echinoderm orders were represented — the Echinoidea by a 
small variety of Echinus norvegicus, v. Diiben and Koren, and a young example of 
Brissopsis lyrifera , Forbes ; the Asteridea by an undescribed species of the genus 
Archaster ; the Ophiuridea by Ophiocten sericeum, Forbes, and Ophiacantlia spinulosa, 
Muller and Troschel ; the Holothuridea by Echinocucumis typica , Sars ; and the 
Crinoidea by a very remarkable new form of the Apiocrinidse, which has been noticed 
under the name of Bathycrinus gracilis, Wyville Thomson. From 2000 fathoms 
upwards the number of Echinoderms seems to increase rapidly; but this apparent 
increase may possibly be due to our greater knowledge of the fauna of shallower water ; 
at from 300 to 800 fathoms along the coast of Britain many species of all the orders 
are enormously abundant, so much so as to give a very marked character to the fauna 
of that special zone. Several of these species (such as Cidaris papillata, Leske, Toxo- 
pneustes drobachiensis, Muller, Echinus norvegicus, D. & K., Astropecten tenuispinus , 
D. & K., Archaster Parellii, D. & K., A. Andromeda, M. & T., Euryale LinJcii, M. & T., 
and Antedon celticus, Barrett) have long been known to inhabit the deep water of the 
British area, and form part of a fauna which will be probably found to have a very wide 
lateral extension at temperatures whose minimum ranges from 0°C. to +2° C. — a fauna 
which crops up, as it were, within the ordinary limits of observation in the seas of Scandi- 
navia, and which has consequently been carefully studied by the Scandinavian naturalists. 
Another group of species (including Tripylus fragilis, D. & K., Ctenodiscus crispatus, 
Betzius, Pter aster militaris, M. & T., Amphiura abyssicola, Sars, Antedon EschrichtiU 
MDCCCLXXIV. 5 E 
