Raymond: notes ox the ontogeny of paradoxides. 229 



In the M. C. Z. there is a complete specimen of P. " pimllus " 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. jmsillus 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 13% 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 1 is present and distinct at the sides. 



Next to this specimen stands our smallest cranidium of P. rugidosus 

 Hawle and Corda, which is 4 mm. long and practically identical with 

 the largest of P. lyusiUus, 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. nirjulosus 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 na 

 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 e^^dence that the line traced above 

 from Hydrocephalus saturnoidcs through Paradoxides orphanus and 

 P. pusillu^ to P. rugidosus represents the growth stages of one species. 

 There are in the collections at the M. C. Z. specimens in all stages be- 

 tween P. pitsillus and the adult P. rugulosus, and the only sharp break 

 is between the largest specimen of Hydrocephalus saturnoidcs 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 



