RAYMOND: NOTES ON THE ONTOGENY OF PARADOXIDES. 227 



forms must therefore belong to another species, which is here de- 

 scribed as P. haywardi. The hirgest cranidium of the rimmed form 

 obtained is 35 mm. long, while the smallest cranidium with the brim 

 and no rim is 19 mm. long (M. C. Z., No. 22, PI., fig. 3). On this 

 specimen the part of the brim in front of the glabella is 2.25 mm. wide, 

 or nearly 12'^"^ of the total length. On a specimen 84 mm. long it is 4.5 

 mm. long, or 1S%, while on a large cranidium, 103 nun. long, it is 

 12 mm. wide, or 11%. On the numerous cranidia between the smallest 

 and largest it varies from 10% to 13% of the length, showing that 

 while it grows wider during the growth of the individual, it is relatively 

 about the same width in all cranidia above 19 mm. long. What it 

 might be in smaller specimens we have as yet no means of knowing. 



The significance of this wide brim on the craniflium of P. harlani is 

 best appreciated after studying the ontogeny of Paradoxides. 



Ontogeny of Paradoxides. 



The smallest specimen of Parado.xides known is that described by 

 Barrande as Hydrocephalus satumoidcs (Systeme Silurien du centre 

 de la Boheme, 1852, 1, p. 380, pi. 49). This specimen is slightly over 

 1 mm. long, the cephalon is 

 oval, and makes up five sixths 

 of the total length. The glabella 

 is large, oval, makes up most 

 of the cephalon, extends to the 

 front of the head, and has no 

 glabella furrows, though there 

 is a median longitudinal furrow. 

 The palpebral lobes form the 

 lateral margins of the cephalon, 

 but judging from the appearance 

 of the cranidium, the free cheeks 

 would have been present even at this early stage, had the specimens 

 been complete. The occipital segment is prominently set off from 

 the rest of the cephalon, and extends to the long, intergenal spines 

 which cross it at right angles. One thoracic segment and a pygidium 

 are present. F'rom the inferred presence of the free cheeks and the 

 presence of a thoracic segment, it is evident that this is not a protaspis, 

 but that several moults have already taken place. 



The second specimen described by Barrande is 1.33 mm. long, the 



Fig. 1. — Hydrocephalus saturnoides, show- 

 ing two of the stages of development. 

 After Barrande. Note the wide, oval 

 glabella. Compare with Plate, flg. 9. 



