235 



In the pygidium, the neopygidium and protopygidium* are distinct ; 

 the former has three rings as strongly marked off as those of the thorax, 

 the protopygidium has the same number of obscure somites. 



In this larval form, which in development is close to the unsegmented 

 larva, the outline of the headshield distinctly recalls the adult in Illsenus 

 and Dysplanus, but the strongly segmented pygidium has an even more 

 generalized meaning. 



Young 6x5 mm. 



This moult already possesses many features of the adult. 



The flattened borders are obvious on both shields, and the headshield is A later mou \^ 

 broken up into the three principal pieces. The movable cheeks have 

 heavy genal spines, and the course of the suture is functionally that of 

 the adult. The slipping of the cheeks in this example has obscured the 

 eyelobe, which, however, appears to be not far from the glabella. The 

 glabella, though slightly marked elsewhere, is marked oft' in front by a 

 slope to the flattened margin. 



The thorax now has five joints, and the pleurae has grooves and facets 

 like the adult. 



The pygidium has about the same number of segments as in the younger 

 shield, but those of the neopygidium are less prominent than in the 

 younger moult ; they are, however, still discernable on the sidelobes, as 

 well as on the rachis. In this, while not agreeing with the genus Asa- 

 phellus, they recall many others of the Asaphidae. 



Size. Length of the whole carapace of the adult, 73 mm,. Length 

 of cephalic shield, 26 mm. ; of thorax, 21 mm. ; of pygidim, 26 mm- 

 Width of cephalic shield, 50 mm. ; of thorax, 43-45 mm. ; of pygidium> 

 45 mm. 



Horizon and locality. In fine gray shale of Assise C. 3 c 2 at McLeod 

 brook, Boisdale, N.S. 



NOTE ON THE YOUNG OF ASAPHELLUS HOMFRAYI. 



Since writing the above in regard to the young of Asaphellus Homfrayi Young of this 

 the writer has consulted Dr. Callaway's article on the fauna of the Shin ton c'onophrys 

 Shales,^ and was at once struck with the resemblance between the 

 youngest form here described, and Conophrys Salopiensis, and it is clear 

 that the latter is a later stage or development of the former. 



* Monograph British Trilobites, p. 165, pi. 24, figs. 6-12. 

 t Quart. Jour. Geol. Soc. London, vol. xxxiii, p. 652. 



* Trans. Roy. Soc. Can. 2me. Ser., vol. iv, sec. iv, p. 145, lines 26, 27. 



