and its Place in the System. 225 



carpus : cacli branch consists of two joints. The fin-rays are 

 attaclicd to the cartilaginous branches exactly in the same 

 way as all the fin-rays of Geratodus or Protoptenis. I may 

 also observe that the " pectoral spine " of the sturgeon does 

 not ditFer, either in structure or with regard to its attachment, 

 from the other fin-rays ; it is formed merely by confluent fin- 

 rays, and can easily be split into two halves. 



Eye without falciform process or choroid gland. 



Ceratodus possesses a Dipnoous heart, as far as the ventricle 

 and (single) atrium are concerned ; but the valvular arrange- 

 ment of the bulbus arteriosus is more of the " Ganoid " type. 

 There is, at a short distance from the origin of the bulbus, a 

 single cartilaginous papillary valve worked by a special 

 muscle ; then follows a transverse series of four small short 

 valves (sometimes reduced to simple papillary prominences), 

 then a series of four oblong raised strips (rudimentary valves?), 

 and, finally, a third transverse series of four well-developed 

 " Ganoid " valves. Four arcus aortas enter the four gills 

 without sending off branches ; and four branchial veins are 

 collected into the aorta descendens. 



The branchial apparatus is composed of five arches, not 

 differing from the Teleosteous type, but cartilaginous ; four of 

 them bear well-developed laraellated gills. The pseudo- 

 branchia does not receive blood which has not previously 

 passed through the gills. Spiracles are absent. 



The lung is single, but its cavity is composed of two sym- 

 metrical halves, each with a row of about thirty cellular com- 

 partments. Pneumatic duct and situation of the glottis as in 

 Lejndosiren. The pulmonal artery is a branch of the arteria 

 coeliaca, and the pulmonal vein enters the atrium separately 

 from the sinus venosus. 



Like Lepidosirenj Geratodus is provided with one pair of 

 vomerine teeth, and two pairs of molar-like palatine teeth. 

 This dentition is modified for a carnivorous diet in the former 

 genus, and for an herbivorous one in the latter, the intestine of 

 all specimens having been found full of leaves of Myrtacese and 

 Graminese. The microscopical structure of the teeth resembles 

 much that of Protoiiterus^ Psammodus^ Dipterus^ and other 

 extinct genera, and is identical with that of the fossil Geratodus- 

 teeth from Triassic and Jurassic formations, confirming the 

 correctness of Mr. Krefft's view, who referred the living fish 

 to the genus which had been established for those fossils. 



Intestinal tract perfectly straight, very wide, with a perfect 

 spiral valve, along the axis of which large glands are im- 

 bedded ; stomach merely indicated by a shallow double pyloric 

 fold ; no pyloric appendages ; spleen represented by a diffuse 



Ann. & Mag. N. Hist. Ser. 4. Vol. vii. 16 



