April 23, 1885] 



NATURE 



575 



rank as to require being ranked as a type of a new family. 

 which, while not specially related to any other Nco- 

 crinoid, presents important characters that connect it 

 with the Pakvocrinoids. 



The Bathycrinus of Wyville Thomson, of which three 

 species are now known, and the Rhizocrinus of Sars, of 

 which the two species now known prove to have a wide geo- 

 graphical distribution, arc next minutely described as mem- 

 bers of the family Bourgeticrinidce (De Loriol). This family 

 represented in the Cretaceous and Tertiary epochs the 

 much more highly developed Apiocrinida of the Jurassic ; 

 and there seems every probability that we can now cor- 

 rectly reconstruct the whole anatomy of the Pear En- 

 crinite on the basis supplied by Ludwig's study of the soft 

 parts of Rhizocrinus, and Dr. P. H. Carpenter's account 

 of those of Bathycri 



We next come to Pentacrinus, the typical genus of the 

 family Pentacrinidce, as this is the typical family of the 

 Every palaeontologist is familiar with the 

 extraordinary development of this family type in the 

 Liassic period, as shown in the splendid slabs exhibited 

 in our museums. The most remarkable species, as 

 regards the length of its stem and the number of the 

 component joints, is Extracrinus su : fossil 



specimens of whose stem have been found to measure 

 from 50 to 70 feet. The mode in which the new joints 

 are added at the summit of this stem was studied by 

 Ouenstedt, as well as the fossilised condition of his speci- 

 mens permitted ; but Dr. W. B. Carpenter has been able 

 to work it out more completely in the recent Pentacrinus 

 wyville-thotnsonij and the excellent figures drawn by Air. 

 George West for the illustration of a monograph of that 

 type which Dr. Carpenter formerly intended to produce, 

 show every successive stage in the development of the 

 segments intercalated at and near the summit of the stem, 

 the gradual assumption by the intercalated segments of 

 the characters of those with which they alternate, and the 

 progressive change from a pentangular to a circular out- 

 line, as well as in their articulating surfaces, which both 

 series finally undergo ; thus making it clear that great care 

 must be used in erecting new fossil species (as has been 

 frequently done) upon the slender evidence of an inch or 

 two of stem. 



Of the genus Pentacrinus, the three species which had 

 been obtained from West Indian Seas before the dis- 

 covery of the European type, had been so variously 

 named and so diversely described, that their synonymy 

 seemed in a state of hopeless entanglement. By a careful 

 comparison, however, of the best-authenticated specimens 

 of each with the large number since collected, Dr. P. H. 

 Carpenter has found himself able to clear up the con- 

 fusion ; this having partly arisen from the wide range of 

 individual variation, especially in a character hitherto 

 regarded as of fundamental importance — the completeness 

 of the basal circlet, and its external conspicuousness, as 

 well as in the number of arms to each ray. The first- 

 known species, originally called his asterias by Linna5us ; 

 now proves to be the rarest ; several of the Museum speci- 

 mens which had been referred to it, being here shown to 

 belong to the species first distinguished by CErsted in 

 1856 as P. miilleri. Greatly exceeding both these in 

 abundance, is the elegant species originally named P. 

 decorus in 1864 by Wyville Thomson, who had obtained 



a specimen of it from Mr. Damon ; the dredgings of the 

 U.S.A. steamer Blake in the Caribbean Sea and the Gulf 

 Stream Channel having brought it up by the hundred, so 

 that, as Prof. Agassiz remarks, " we must have swept 

 over actual forests of Pentacrini crowded together, much 

 as we find the fossil Pentacrini on slabs." Another 

 species, /'. blakei, was dredged by the Blake at four sta- 

 tions in the Caribbean Sea ; and neither of these four 

 rpecies has been met with elsewhere. Of the P. wyville- 

 , which first presented itself in the Porcupine 

 dredging of 1S70, thirty specimens were recently dredged 

 by the Talisman (French) at a depth of 800 fathoms off 

 Rochefort ; but it was not anywhere met with by the 

 Challenger, which, however, brought up a specimen of a 

 beautiful new species, P. madearanus, from the Tropical 

 Atlantic, several specimens of two types respectively- 

 named P. naresianus and P. alternicirrus, from the 

 Western Pacific, and a single mutilated specimen from 

 the Japan Sea of a doubtful type, which, on account of 

 the deficiency of calcareous material in its calyx, Dr. 

 P. H. Carpenter provisionally names P. mollis. All 

 these species appear to have but a limited geographical 

 range ; and this seems also to have been the case with 

 the fossil species of the Lias, the British and Continental 

 species being mostly different. These, too, have a limited 

 geological range ; no species occurring in all its three 

 divisions, and only two out of the fifteen which are found 

 in the middle and upper Lias of this country being 

 common to those two divisions. 



Of all the stalked Crinoids, it is Pentacrinus (as was 

 seen by J. S. Miller) which bears the closest resemblance 

 to the unattached Comatula; the chief difference being 

 that the basals of the pentacrinoid larva are retained in 

 the adult Pentacrinus, whilst they disappear externally in 

 Comatula, inward 'prolongations of them coalescing to 

 form the curious "rosette" first described by Dr. W. B. 

 Carpenter. In regard to their mode of life, there seems really 

 very little difference between these two types ; for obser- 

 vation of the habits of living Comatulm shows that they 

 only perform their beautiful swimming movements in 

 order to find a suitable base to which they can attach 

 themselves by their dorsal cirri ; whilst on the other 

 hand it seems quite certain that the stalked Pentacrini 

 are not unfrequently detached by the fracture of their 

 stems just below one of its nodal joints, and that the 

 cirri which spring from the latter then bend downwards 

 and cling to any suitable attachment, just like the dorsal 

 cirrhi of Comatula. The structure of the visceral disk 

 as well as of the arms and pinnules of Pentacrinus, has 

 been found by Dr. P. H. Carpenter to bear the closest 

 similarity to that of the corresponding parts in Comatula; 

 and while the five-chambered organ at the base of the 

 calyx, from the walls of which the primary nerve-trunks 

 radiate, is much smaller in Pentacrinus than in Comatula 

 (its greater size in the latter being obviously related to the 

 number of verticils of cirral nerve-cords it has to give 

 off), a similar dilatation of the Crinoidal axis presents 

 itself in each node of the stem, giving off from its exterior 

 a single such verticil. 



It is not a little curious that in the Eastern Archipelago 

 and the neighbouring part of the Pacific, Pentacrinus is re- 

 placed by a new generic type, closely allied to it in the 

 most essential features of its structure, to which Sir 



