KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 21. N:0 9. 31 



phylogenetical clevelopraent, been suhject to a kind of retrograde metamorphosis or de- 

 generation; so that instead of proceeding from lower to higher forms, they have developed 

 in a contrary direction. In the Dgenealogical tree» of the Arachnida constructed by 

 Ray Lankester, the Solifugte, Chelonethi and Acari form, in fact, the last or upper- 

 most branches of the stem of the Class. The possibility of this mode of development 

 cannot, of course, be denied. It presupposes that the Merostoms form a much more 

 ancient branch of the group of the Arthropoda, than the Arachnida, and that these 

 have branched off from the Merostoms comparatively late in the precambrian age. But 

 may not the development of, at least, the bulk of the Arachnida be more probably one 

 from lower to higher forms; from Acari ^), or, rather, from animals related to the Che- 

 lonethi or the Opilions, and breathing with tuhular trachete, through the Meridogastra 

 or Anthracomarti ^) to the Spiders, the Pedipalpi and the Scorpions, which breathe with 

 lamellur trachete? In this case also, the Arachnids would form a very ancient type, and 

 the common origin of the Merostoms and the Arachnids must be sought for far down 

 in the pedigree of the Arthropods. The agreement between Scorpions and Eurypterids 

 would then be derived from causes quite independent of close relationship, and per- 

 haps from a convergence in some branches of the two stems which are formed by the 

 Merostoms and the Arachnids. — 



The remarkable genus Glyptoscorpius Peach^) from the Carboniferous rocks of 

 the Scotch Börder, is unfortunately so imperfectly known that it is irapossible even 

 approxiraately to fix its systematic position. Peach, who regards the forms belonging 

 to this genus, as transitions between the genuine, Silurian Eurypterids, which lived 

 in water, and the Scorpions, classes them with the former group, notwithstanding 

 that he considers them to be land animals and closely related to the Scorpions*). 

 The species of Glj'ptoscorpius in a high degree remind one of the true Euryp- 

 terids, not only by the peculiar sculpture of their integument, but also by their 

 occasionally large size: a dorsal plate of G. Caledonicus (Salter) is said to measure 

 more than one foot across. Their integument is »not crustacean in its character, but 



') It is however not improbable that the Acari, and possibly also the Solifugaa, have had an origin different 

 from that of the Scorpions and the Spiders etc., as is probably also the case with the Cormopoda (Tar- 

 digrada or Arctiscoidas), the Acauthotheca and the Pantopoda (Pycuogonoidae), even on the snpposition 

 that the last-meutioned animals are really Arachnids. 



Compare Thorell, Étndes Scorpiologiques, in the Atti della Soc. Ital. di Storia Natnrale, XIX (1877), 

 pp. 86 et sequ. The Class of tlie Arachnida is in this memoir snbdivided in the foUowing manner: »Sub=- 

 class. I. Thoracopoda: Ord. 1. Scorpiones, 2. Pedipalpi, 3. Aranese, 4. Opiliones, 5. Solifugse, 6. Pseudo- 

 scorpiones (= Chelonethi), 7. Acari, 8. Linguatnlina (= Acanthotheca); Sub-class. II. (Ord. 9) Cormo- 

 poda». — Eay Lankester (Limulus an Arachnid, 1. c, p. 86) classifies the Arachnida as follows: »Grade 

 A. Hcematobranchia (= Merostomata) : Ord. 1. Trilobita, 2. Enrypterina, 3. Xiphosura; Grade B. Aero- 

 branehia: Ord. 1 (4). Scorpionina, 2 (5). Pedipalpi, 3 (6). Araneina; Grade C. Lipobranchia : Ord. 

 1 (7). Solifngfe, 2 (8). Pseudoscorpionina, 3 (9). Opilionina, 4 (10). Acarina». — The Cormopoda and 

 the Acanthotheca are not by Eay Lankester numbered among the Arachnida. 



-) As Anthracomartus Karsgh is the name of a genus, Anthracomarti does not seem to be a suitable name 

 for the Ordei' which embraces that genus and several others. We propose to name it Meridogastra, (from 

 !.isQi.c, part, and yaair^Q, abdomen). 



•') Fnrther Kesearches among the Crustacea and Arachnida of the Scottish Börder, in Transact. of the Roy. 

 Soc. of Edinburgh, XXX, Part n, pp. 516 et .sequ. (1884). 



*) Peach also regards »the Carboniferous Eurypterns» — probably iJ. &'oh/<?77 Hibb., the extremities of which 

 are almost entirely unknown — as a land aiiimal and nearly related to Glyptoscorpius. 



