9G Forty-fourth Report on the State Museum, 



given by Corda. The median lobe of the glabella is small, the lateral 

 lobes, instead of being more or less distinctly in two pairs, are con- 

 fluent and exceedingly irregular; the occipital ring is devoid of spines 

 or conspicuous tubercles and the long cheek spines take their origin 

 above the genal angles and on the upper surface of the cheeks. Tlie 

 thoracic segments are very broad, each annulation bearing at its 

 junction with the pleura a very strong node; the pleural ridges are not 

 direct as in other species, but cross the entire width of the pleurae 

 obliquely from below upward and are there recurved into very long 

 spines. The pygidium is described by both Corda and Barrande as with- 

 out marginal spines and hence Corda's name. But Barrande has figured 

 one very imperfect specimen retaining a single spine and in the figure, 

 here copied, they were drawn in dotted lines. The cephalon is also 

 without marginal spines. A comparison of these features with those 

 of the other groups already indicated leaves no doubt that the single 

 example of this type of structure stands well apart from its allies. 



In the same year that Corda's " Prodrom " appeared (1847) the 

 term Polyeres was used by Kouault* in a list of the palaeozoic fossils 

 found in the vicinity of Rennes, Brittany, for a trilobite which Barrande, 

 after a personal inspection of the specimens, pronounced identical 

 with his Acidaspis Buchi. Bouault's description of his genus was very 

 brief. The essential character upon which it was based being the 

 long thoracic spines. The single species mentioned, Polyeres Dufrenoyi, 

 Rouault, was not figured. It must be admitted that from the original 

 description alone of Polyeres it would be difficult to recognize its 

 value, but the opinion expressed by Barrande fully determines its 

 worth. As it is necessary to choose between the two terms Seleno- 

 PELTis and Polyeres proposed the same year, it seems the wiser course 

 to accept Corda's name, which was not only clearly defined but was 

 also illustrated, f 



It appears from the foregoing that many of the generic names 

 which have been proposed for the trilobites known as Acidaspis, have 

 a certain permanent value. If we admit these terms in a classifica- 

 tion, the subdivision of the entire group of Ceratocephala is found 



* Bulletin de la Societe g^ologique de France, 2 ser. vol. 4, p. 320. This paper was read 

 at the session of December, 1846, and its date is thus quoted by both Barrande and 

 Vogdes. The cover of these feuilles 20-25 bears the date of April, 1847. 



t In spite of the serious indisposition toward Corda's work evinced by Barrande, a 

 feeling which is explained by the circumstances connected with the appearance of this 

 monograph, it becomes increasingly evident that it contains many kernels of good 

 grain, though concealed among much chaff. The chaff has been sufficiently brought 

 to the foreground. It is obligatory upon students of palaeontology to lose sight of the 

 personal differences of a passing generation and uphold the truths that this investi- 

 gator was fortunate enough to elicit. 



