168 RAMSAY H. TRAQUAIR ON 
was, however, observed by Professor Youne, and he states that the jugular 
plates are “in two pairs, principal and posterior,” and that there is no trace of 
median or lateral plates. The characters of the scales and of the vertebre, 
whose centra are in the form of osseous rings, are described as well as the 
dentition ; the teeth of the maxilla being fine, equal, and conical, while those of 
the mandible are of two sizes. The non-trenchant character of the mandibular 
laniaries distinguishes the genus from &/izodus, while as separating it from 
Holoptychius, Professor Youne gives the thinness of the scales, the nature of 
their ornament, and the presence of teeth of two sizes. 
Two years later a notice of this fish was published by Messrs Hancock and 
ATTHEY, from specimens found in the shales of the Northumberland Coal Field,* 
in which the authors state that in all respects their specimens “agree well with 
Dr Youne’s description of the species.” Their description contains, however, 
two points specially worthy of notice, viz., the detection, on the anterior 
margins of some of the fins, of peculiar fulcral scales similar to those which 
occur in Megalichthys and other Saurodipterines, and the determination of a 
peculiarly shaped dentigerous bone as “pramazilla.” Moreover, according to 
Messrs Hancock and ATTHEY, the piscine genera and species Dittodus parallelus, 
Ganolodus Craggesii, and Characodus confertus, and the supposed Amphibian 
Gastrodus, all founded by Professor OWEN on specimens of teeth from the same 
coal-field, are only synonyms of Rhizodopsis sauroides. 
Rhizodopsis is also noticed by Mr T. P. Barxas,t who accepts Messrs 
Hancock and ATTHEY’s interpretation of the bone supposed by them to be a 
premaxilla. So also does Mr J. W. Barxkas,{ who solves the problem 
regarding the specific nomenclature of the fish by quoting Rhizodopsis sauroides 
and granulatus as distinct species, without, however, giving any reasons in 
support of the supposed distinction. 
Being struck by the total dissimilarity of form presented by the bone 
interpreted by Messrs Hancock and ATTHEy as the preemaxilla of Rhizodopsis, 
when compared with that element in other Crossopterygii, I carefully examined 
the subject with the aid of a beautiful series of specimens from North Stafford- 
shire, kindly lent me by my friend Mr Joun Warp, F.G.S., and with the result 
of finding that the reputed premaxilla is in reality the dentary element of the 
mandible. Moreover, the mandible of &hizodopsis is of a very complex 
structure, and that structure finds itself in all essential respects repeated and 
explained in the mandible of the much more bulky Rhizodus Hibbert. 
These observations were published in the ‘“ Annals and Magazine of Natural 
* “Note on the Remains of some Reptiles and Fishes from the Shales of the Northumberland 
Coal Field,” Ann. Nat. Hist. (4), vol. i. (1868), pp. 346-378. 
+ “Manual of Coal Measure Palontology,” London, 1873, pp. 23-25, Atlas, figs. 59-66. 
t Monthly Review of Dental Surgery, vol. iv. No. x., March 1876. 
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