- RAYMOND: NOTES ON THE ONTOGENY OF PARADOXIDES. 229 
In the M. C. Z. there is a complete specimen of P. “ pusillus ’’ which 
is 4.5 mm. long, or about twice as large as the one figured by Barrande. 
The cephalon is 2 mm. long, or 44% of the whole length, and the brim 
is narrower than in the last specimen. Both the genal spines and 
those of the second thoracic segment are long, but the first thoracic 
segment has lost its spines. ‘There are about fifteen thoracic segments 
ending in free spines, but those back of the tenth are crowded into an 
extremely small space. (See Plate, fig. 9). 
The largest cranidium of P. pusillus in the collection is 4.5 mm. long, 
and Barrande does not mention any larger. In this largest specimen 
the brim is only .5 mm. wide, thus occupying but 18% of the length, 
showing that with increase in size the brim is becoming shortened 
again. Furrows 3 and 4 cross the glabella, while 2 does not. Fur- 
row | is present and distinct at the sides. 
Next to this specimen stands our smallest cranidium of P. rugulosus 
Hawle and Corda, which is 4 mm. long and practically identical with 
the largest of P. pusillus, but furrows 2 are a little more faint, furrows 
4 turn more obliquely backward, and the posterior ends of the palpe- 
bral lobes are a little closer to the glabella. From this small specimen 
we have all gradations up to a full-grown P. rugulosus with a crani- 
dium 27 mm. long. In the adult P. rugulosus the anterior furrow is 
very narrow, the glabella being almost in contact with the rim. 
Whether this line of development is based entirely upon one species 
or not, the fact remains that in the development of the brim of Para- 
doxides there is a change from the very youngest where there is no 
brim to a youthful stage where the brim is wide, then back to a later 
adult stage in which the brim is again diminished almost to nothing. 
In the matter of the brim, therefore, P. harlani retains at maturity a 
youthful characteristic, lost in P. rugulosus when less than.10 mm. 
long. 
There is a certain amount of evidence that the line traced above 
from Hydrocephalus saturnoides through Paradoxides orphanus and 
P. pusillus to P. rugulosus represents the growth stages of one species. 
There are in the collections at the M. C. Z. specimens in all stages be- 
tween P. pusillus and the adult P. rugulosus, and the only sharp break 
is between the largest specimen of Hydrocephalus saturnoides and the 
smallest of P. orphanus or P. pusillus. In the matter of the brim there 
is no break, for we see it gradually becoming wider and wider in speci- 
mens of H. saturnoides, it continues getting wider in P. orphanus and 
P. pusillus up to a certain stage, then decreases in width in the larger 
pusillus and the young of rugulosus. The only great change between. 
