230 bulletin: museum of comparative zoology. 



Hydrocephalus saturnoides and P. orphanus is the introduction just 

 at this point of the anterior pair of glabellar furrows and the reduction 

 in size of the glabella. But the furrows come in where we would 

 have predicted them, just in front of the palpebral lobes. And this 

 brings out a point, which was wholly unexpected, that in this species 

 of Paradoxides the glabella of the youngest specimens known is smooth 

 and unsegmented, and gains its furrows during growth. This will be 

 referred to again later. 



There are also external indications which indicated that the above 

 series may be a natural one. Hydrocejyhalus saturnoides, P. orphanus, 

 and P. pusillus all palpably represent immature individuals and have 

 been generally so considered. Hydrocephalus was placed by Barrande 

 as akin to Paradoxides, and by Beecher was referred to that genus. 

 Barrande separated it from Paradoxides, first, on account of the course 

 of the facial suture, which left the genal spine on the fixed instead of 

 the free cheeks ; second, on account of the longitudinal furrow on the 

 glabella; and third, because of the few thoracic segments, there 

 never being more than twelve. 



The third characteristic merely indicates immature specimens and 

 need not be considered. In regard to the second one of the remarka- 

 ble features of P harlani is that this same longitudinal furrow of the 

 glabella is present, at least as a line of weakness, in very large speci- 

 mens. As to the first, the spines on the fixed cheeks are merely the 

 terminal spines of the palpebral lobes, the intergenal or " interocular " 

 spines known also in the young of Olenellus. From the form of the 

 cranidium it is evident that entire specimens had free cheeks, and 

 they doubtless bore the true genal spines. There is, therefore, no 

 reason for separating Hydrocephalus from Paradoxides. 



In regard to occurrence, all four species come from the Cambrian 

 band in the vicinity of Skrey, and so far as known are found together 

 in the same beds. Most of the specimens of H. saturnoides in the 

 M. C. Z. collection are from Teirovic, from which locality there are 

 also specimens of P. pusillus and P. rugulosus. All are in the same 

 kind of matrix and have the same sort of preservation. At Slap, 

 where P. rugulosus is most abundant, H. saturnoides seems less com- 

 mon, though P. pusillus is quite common. 



Of the Bohemian species, P. sacheri Barrande, P. lyelli Barrande, 

 P. bohemicus (Boeck) , and P. rotundatus Barrande seem to be confined 

 to the Ginetz band of the Cambrian, hence it is unlikely that these 

 young should belong to any of those species. Paradoxides spinosus 

 (Boeck) is very common in the band of Skrey and when I began to 



