164 G. P. MATTHEW : ILLUSTEATIONS OP 



side of the head to the glabella near the anterior end. ' An examination of the plates 

 appended to this article, will shew that in the trilobites of the third group, the mode of 

 development of the eyelobe was different. The family of Paradoxides exhibits also at a 

 very early stage an expanded border rim outside of the arc of the ocular lobe, but in the 

 Conocoryphinœ and Ptychoparinœ the anterior border, when it first appears, is narrow, 

 weak and close to the glabellar lobe. These differences are sustained by those in other 

 points of the structure as the hypostome, pygidium, etc , and together shew clearly the 

 independence of the family of the Paradoxides. 



The Paradoxides of the St. John group have representatives of several sections of the 

 genus, some with continuous eyelobes, belonging to Band c ; others with shortened eye- 

 lobes, which are in the upper jiart of Band c and in d. P. lamellatus, is one of the oldest 

 known in the St. John Basin, but though the eyelobe is somewhat shortened in the 

 broad form, it is continuoiis in another variety (the narrow form ?), and the species carries 

 a hypostome which allies it more closely with the associated species having continuous 

 eyelobes, than with those whose eyelobes are decidedly shortened ; the posterior corners 

 of the hypostome carry long spines, and the doubleur of the front rim is detached. 



From the study of the Paradoxides of the St. John gi'oup, it appears to the writer that 

 a granulated test is to be looked upon as indicative of the oldest type in this genus, 

 though in the best known forms, this is not the condition of the surface of the test, 

 nor is it so in the species upon which the genus was established. Among the earliest 

 species of the St. John Basin, there are two granulated species, and these exhibit a ten- 

 dency to acquire a wrinkled surface, either in the later stages of growth, or in varieties 

 that originated after the typical form. The progressive changes in the glabella of P. 

 I'ameUatus in this respect, were described in these Transactions for the year 1884 (Sec. 

 IV, p. 100) and a wrinkled variety of P. Acadiais in the same transactions for 1885 (Sec. 

 IV, p. 7Y.) Nevertheless, the earliest examples of P. Eteminicus and P. Micmac, wrinkled 

 species, do not exhibit a tendency to a granulated surface. 



A hypostome, subrectangular at the base, devoid of heavy spines at the posterior 

 angles, and possessing an anterior border or doubleur serves to distinguish the two later 

 species of Parodoxides from the others. These two species, however, are separated from 

 each other by other very important characters. 



Finally, it is worthy of notice that in the development of the young of the Ptycho- 

 paridœ there is a confirmation of the view expressed in a former "' paper as to the impor- 

 tance of the early changes of form in the trilobites. If the development of species, as 

 exhibited in the embryonic and larval forms of Agraulos, Liostracus and Soleuopleura, 

 figured in the accompanying plates, be examined, the very great importance of these early 

 stages, as shewing the plastic condition of the organism in the initial metamorphoses is 

 readily seen. One has only to note in the series of embryonic and larval forms how different 

 the embryos are from the adult ; and yet to observe also how soon the generic and even 

 the specific types become visible in the larval head-shield, to be satisfied that the main 

 potentiality of development is in the embryo and the embryonic stages of the organism. 



The author cannot close this paper without paying a tribute to the very excellent 



' S. W. Ford shows that the eyelobe in the young of Olenellus had a similar form. 

 = Trans. Eoy. Soc. Canada, 1882, Sec. iv. p. 107. 



