1872.] On the Echinidea of the x Porcupine ' Expeditions. 491 



hydride and olefine containing an equal number of carbon atoms as in the 

 above equation. Neither supposition is exactly substantiated by experiment. 

 If the action of heat gave rise to the former mode of decomposition, we 

 ought to obtain a larger quantity of ethylene after prolonged heating, 

 especially when the liquefied portion is rich in hydrocarbons of low mole- 

 cular weight ; but it has already been pointed out that the process of 

 liquefaction is accompanied with the production of comparatively little gas. 

 On the other hand, an examination of the amounts of bromine required to 

 render the hydrocarbons boiling above 200° permanently red, shows that 

 the proportion of hydride to olefine in the several mixtures becomes gra- 

 dually larger as the molecular weight increases. 



It would doubtless have been interesting to have determined the relative 

 amounts of the twelve fractions isolated from the decomposed paraffin ; but 

 when it is considered that their separation was only effected after several 

 thousand distillations, it will be evident that the quantities obtained after 

 such prolonged treatment can afford no real indication of the amounts 

 present in the original liquid. It appears, however, that the amounts of 

 liquid boiling at 94-97° and 122-125° were but slightly, if at all, less than 

 the quantities boiling at 252-255° and 273-276°. 



XIX. " On the Echinidea of the ' Porcupine ' Deep-sea Dredging-Ex- 

 peditions." By Prof. Wyville Thomson, LL.D., D.Sc, F.R.S. 

 Received June 15, 1872. 



(Abstract.) 



The deep-sea dredging-cruises of H.M. Ships 'Lightning' and Porcu- 

 pine 9 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 Fseroe 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 depth Echinodermata appeared to be abun- 

 dant. At 2435 and at 2090 fathoms all the Echinoderm orders were repre- 

 sented — the Echinidea by a small variety of Echinus norvegicus, D. & K., and 

 a young example of Bj'issopsis lyrifera, Forbes ; the Asteridea by a species 

 of the genus Archaster ; the Ophiuridea by Ophiocten sericewn, Forbes, 

 and Ophiacantha spinulosa, M. &T. ; the Holothuridea by Echinocucumis 

 typica, Sars ; and the Crinoidea by a very remarkable new form of the 

 Apiocrinidae, which has been described under the name of Bathycrinus 

 gracilis, Wy. T. From 2000 fathoms upwards the number of Echino- 

 derms seems to increase rapidly ; lir.t this apparent increase may possibly be 



