. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 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 mm. wide, or nearly 12'^"^ of the total length. On a specimen 84 mm. long it is mm. long, or 1S%, while on a large cranidium, 103 nun.
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 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 mm. wide, or nearly 12'^"^ of the total length. On a specimen 84 mm. long it is 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 The smallest specimen of 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
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