MACROPOMA MANTELLII. 29 



the dorsal fia rays are constructed in this manner 



There are two dorsal fins ; the first is situated immediately behind the 

 pectoral girdle ; its rays are long and very strong. The second, situated 

 opposite [en face] the anal (PI. 65 a), has rays which are less robust, 

 shorter, and more numerous, borne by a great bifurcated interspinous 

 bone. In this specimen the fin has not fewer than 13 rays. The 

 ventrals and the anal are nearly of equal size ; the ventrals are opposite 

 the middle of the space comprised, between the two dorsals ; the anal is 

 rather further back than the second dorsal. Both are composed of 

 very short, but strong rays. 



" The caudal is extremely broad, and if, as everything seems to show, 

 it is entire in the specimen (PI. 65 a), it offers a most curious type of 

 structure, a kind of great fan, all of whose rays appear to be equal. 

 It is probable that it was rounded, as in certain Sauroids, at least no 

 difference is observable between the upper and the lower rays. This 

 fin is, in addition, supported in equal proportions by the superior and 

 inferior caudal spinous processes, and the vertebral column is nowise 

 bent upwards, as is the case in all the inasquilobed Ganoids. Its rays 

 are very strong. I have counted some twenty in the lower, and a few 

 more in the upper lobe. All are nearly equal, and only the anterior 

 ones, situated at the base of the fin, are a little shorter. Their structure 

 is the same as in the other fins, that is to say, the visible part of the 

 ray is supported by a shorter ray, which is itself supported by the 

 spinous processes of the vertebras. The greater part of the caudal 

 vertebras thus afford support to the caudal fin, and it is this which 

 gives the fin its great width. 



" The internal skeleton of our M. Mantelli is in general robust. 

 The apophyses are short but large, at least in the neighbourhood of the 

 tail ; those of the abdominal vertebras are longer, and bent more back- 

 ward. The vertebras, on the other hand, are small and delicate 

 relatively to the size of the fish. 



" But our knowledge of this remarkable fish is not limited to the 

 skeleton ; many of the soft parts are also preserved. Among others, 

 there are, in Mr. Mantell's collection, many specimens of the trunk in 

 which the stomach is distinctly recognizable. (PI. 65 c, fig. 1, and 

 PI. 65 d, fig. 1.) It resembles a squamose cylinder, an appearance 

 which is evidently the result of the changes which have taken place 

 in the different membranes which compose its walls ; vascular trunks 

 can even be perceived. These remains are commonly accompanied by 

 coprolites, which have evidently been formed in the intestine. They 

 have a general resemblance to those of Sauria, and are sometimes 

 grooved in the same way. I have represented a series of them in 

 Plate 65 a, to show the variety of forms which they affect. It is these 

 coprolites which have been described by many authors as petrified fir- 

 cones." (P. 177.) 



In the explanatory notes which follow Prof. Agassiz speaks of 

 the " bassin," without describing it, and of the " plaque qui tient 

 lieu de rayons branchiostegues." 



When Professor Agassiz published his " Monographie des 

 Poissons Fossiles du Vieux Gres Rouge," his views respecting the 

 systematic position of Macropoma appear to have undergone con- 

 siderable change. Thus he observes, at p. 61 : — 



** J'ai deja fait remarquer que le genre Macropoma de la craie, ainsi 

 que le genre Undina de M. le Comte de Minister, cadrent mal avec les 



