174 DISTRIBUTION. 



I have sought in vain, however, for the evidence on which this citation rests, tlioiigh there 

 is no a priori reason why the case should not be accepted as authentic.^ 



Fossil Hydroid MeduscB. — If we except the graptoHtes, which will be afterwards considered, 

 the instances now mentioned are the only ones yet known of any portion of an undoubted 

 hydriforra trophosome having been preserved in a fossil state. Among the most interesting 

 evidence, however, of ancient hydroid life, is that afforded by the discovery of fossil hydroid 

 medusae. 



Several medusae — some true hydroid or gymnophthalmic forms, and others belonging to the 

 Discophora or steganophthalmic group- — are now known to exist as fossils. These are all of 

 Jurassic age, having been found only in the lithographic slates of Solenhofen and Eichstadt, and 

 it is to Haeckel that we are indebted for most of our knowledge regarding them. 



In 1845 a fossil medusa was exhibited by Frischmann, at a meeting of the Nuremberg 

 Association of Naturalists, and was soon afterwards briefly described by Beyrich under the name 

 of JcalepJia deperdita." HaeckeP has since subjected this fossil to a careful examination, and, 

 under the name of Craspedites deperdita, has given a figure and full description of it. He regards 

 it as a hydroid medusa, and refers it to the family of the Traclii/tiemida. He afterwards^ alters 

 the generic name from Craspedites to Trachynemites. 



The fossil belongs to the white or upper Jurassic formation of Eichstadt, in Bavaria, and is 

 one of the most perfect impressions of medusae known. Four specimens of it have been found, 

 and are distributed among the museums of Munich, Carlsrhue, and Berlin. The largest specimen 

 has a diameter of two inches seven lines, and presents the form of a disc bounded by a circular 

 furrow, and showing another furrow internal to this, concentric with it, and separated from it by 

 a distance of five lines. From eight equally distant points of the inner circle there run eight 

 straight radial furrows towards the centre, without, however, reaching it. Each radial furrow is 

 deeper and wider in the middle of its length than at either end, so that the convex cast on the 

 obverse slab has each radiating line projecting almost in the form of a lanceolate leaf. 



The obvious interpretation of these appearances leads Haeckel to view the central area into 

 Avhich the radiating furrows do not extend as corresponding to the place of the manubrium and 



' It is quite possible that the Websleria crisioides of Milne-Edwards is a hydroid. Under this 

 name M. Milue-Edwaids (' British Fossil Corals/ part i, p. 43, tab. vii, figs. 5, 5a) has described a 

 fragment of a fossil discovered by Mr. Frederick Edwards in the Loudon Clay of Hampstead. He 

 regards it, though with some doubt, as an actinozoon, referring it to the family of the Gorgonidce. 



Judging from M. Milne-Edwards's figure and description, the resemblance of Websteria crisioides 

 to a sertularian hydroid, notwithstanding obscure indications of a central axis, is considerable, certainly 

 greater than to a gorgonidan. I have endeavoured, in vain, however, to obtain a sight of the original 

 and only specimen yet found. This seems to have been lost, and without an actual inspection I 

 should scarcely feel justified in expressing an opinion as to its affinities. 



M. Pictet (' Traite de Paleontologie ') is also disposed to believe in the possible hydroid nature of 

 Websteria. 



' It would seem, however, that the first notice of this fossil was given in 1835 by Fr. S. 

 Leuckart, who correctly referred it to the impression of a medusa. See Rud. Leuckart, in ' Wieg. 

 Arch.,' 1870, Band, ii, Seit 279. 



' 'Zeit. f. Wissens. Zool.,' 1865, vol. xv, p. 506, tab. 39, fig. 1. 



^ Id., vol. .\ix, p. 560. 



