DISTRIBUTION IN TLME. 175 



nioutli, and the eiglit radiating furrows as the remains of the radiating canals.' Tiie inner of the 

 two concentric circles is regarded by Ilaeckel as the circular canal, and the outer as the periphery 

 of the umbrella, which has become compressed by the conditions to which it' had been exposed 

 after death. The dilatations at the middle points of the radiating canals would represent the 

 generative appendages of these canals. The uud)rella margin is even, showing no trace of a 

 division into lobes. 



The living genus to which Ilaeckel regards the fossil as most nearly allied is Bhopalunrma. 

 This, when viewed from the summit, presents quite the same essential relations of form as the 

 fossil, having eight radiating canals, each carrying at its middle point a sexual sac ; and this view 

 is further strengthened by the fact that in Rhopalonema the radiating canals are, according to 

 Haeckel, supported by a double cartilaginous band, specially fitted to leave behind a well-marked 

 impression, while the umbrella itself in the Trachpiemida, to which Rhopalonema belongs, 

 possesses an almost cartilaginous consistence, and is thus peculiarly adapted for preservation in a 

 fossil state. 



The large size of Traclii/nemiies dcperditus, when compared with any living Traehynemidan, 

 is remarkable, the largest known living Traehynemidan measuring little more than a quarter of 

 an inch in diameter, while the fossil has a diameter of more than two and a half inches. 



The only other hydroid medusa which has been determined with sufficient certainty from 

 its fossil imjjression has been referred by Haeckel, to whom we are indebted for our knowledge 

 of it, to the family of the ^Ei/inidcs.^ Tiie impression, which is very distinct and sharp, occurs 

 on a slab of the lithographic slate of Solenhofen, forming part of the collection in the Palaeonto- 

 logical Museum at Munich. It exhibits both umbrella and marginal tentacles. The umbrella is 

 one inch and a half in diameter, with eight marginal lobes. The marginal tentacles are admirably 

 preserved. These are eight in number, and can be traced to the intervals between the marginal 

 lobes of the umbrella. They are eight inches in length, cylindrical, and about a quarter of an 

 inch thick for the greater part of their length, when they begin to taper to a point at their distal 

 extremity. They are traversed in their entire length by a reddish-brown line, which there is 

 every reason to interpret as the remains of an axial canal. From the peculiar way in which the 

 tentacles lie in the fossil, and the stiff curves into which they are thrown, it appears that in the living 

 animal they must have possessed considerable rigidity, a condition which is very characteristic of 

 the marginal tentacles in the living jEfinidte. Indeed, both umbrella and tentacles in the 

 ^pniddB possess for the most part a cartilaginous consistence, which renders them particularly 

 well fitted to come down to us in a fossil state. 



If we follow in the fossil the direction of the axes of the tentacles, when prolonged towards 

 the summit of the umbrella, we may distinguish eight small pit-like depressions at a distance of a 

 little more than a quarter of an inch from the margin. These appear to be the impressions of 

 the eight sexual sacs. No trace exists of mouth or stomach, or of the lateral gastric pouches 

 which characterise the living yE^inida. 



Ilaeckel assigns to this fossil the name oiFalcpgina (jigantea. In referring it to the family of 



' Rud. Leuckart, however (' ■Wiegra.-uin's Archiv,' 1870, Band ii, Seit 280), asserts, from an actual 

 inspection of the Carlsriihe specimen, that the eight radiating furrows regarded by Haeckel as 

 impressions of the radiating canals, are in this specimen approximated to one another in pairs, and thus 

 throw doubt upon the validity of Haeckel's determination. 



" Ilaeckel, ' Zeit. f. Wissensch. Zool.,' vol. xix, p. 540, tab. 40. 



