THE FAUNA OF THE ST. JOHN GEOUP. 133 



2nd Stage (Plate I, fig-. 2 i.) — lu this, which is a larval stage, the long glabella with 

 deep dorsal furrows, readily distinguishes this species from Liostracus, and ou the mould, 

 the furrows of the glabella are seeu to have nearly attained their relative positions, as seen 

 iu the adi^lt, but the glabella leaves as yet but a very narrow limb between it and the 

 anterior marginal furrow. 



Srd Stage (Plate I, fig. 2 A:). — Here the glabella is shorter, the eyelobes carried further 

 back, the anterior limb of the cheeks fairly developed, and the middle piece of the head- 

 shield exhibits in its outline more clearly the truncate-pyramidal form of the corresponding 

 part of the test in the adiilt. 



4th Stage (Plate I, fig. 2e.) — This is probably is a young individual of the broad 

 form. The size and outline of the glabella in this form is fairly represented ; in another, 

 of about the same size, the glabella is proportionately longer, and though somewhat 

 conical, may be that of an individual of the narrow form. 



The broad form, in its early stages, with its depressed front, strong occipital spine, and 

 sloping sides, has an Agrauloid aspect, but the glabella is longer and more prominent than 

 in Agraulos proper, and in the adult is unusually large in comparison with the cheeks 

 (Plate I, fig. 2 d.) 



The adult, narrow form (Plate I, fig. 2 a.) is clearly distinguishable from the two species 

 of Liostracus, but in the early stages, these two genera are wonderfully alike. We cannot 

 doubt, therefore, that there is a close relationship between them, and when all the parts of 

 this species are recovered, it may prove to be a Liostracus, though, at present, the tumid 

 anterior limb of the fixed cheek and other characters preclude us from placing it there. 



Localitij and Horizon. — In the fine, grey shales of Div. (Stage) Ic at Portland, Simond's, 

 and St. Martins. Not common. 



This species I at one time thought the form which Prof. Hartt designated Conocephalites 

 Hallii, but Mr. Walcott declares that Hallii is a synonym for C. Orestes, and the figure he 

 gives of the type specimen of P. Hallii bears out this statement. Mr. "Walcott's figure ' 

 does not show any occipital spine, and, unless it is mutilated, cannot represent the species 

 I have described above. This species is named in place of Conocephalites Hallii, Hartt, 

 which is thus found to be a synonym, and is so named, to carry out Prof. Hartt's intention 

 of commemorating the name of the eminent palseontologist of the New York Survey, in 

 connection with this fauna. 



Among the species associated with it, it is distinguished from Sotenopleiira Robbii, and 

 its var. Orestes, by the possession of a fixed spine on the back of the occipital ring, and 

 from the two Liostraci, by the tumid anterior limb of the fixed cheek iu place of the 

 channelled space which these possess. 



Among foreign species it differs from A. strenuus, Bill., A. difformis, Aug., and A.primœvus, 

 Brôg., in the shorter eyelobe, and in other respects, and from A. quadrangidaris, Whitfield, 

 in possessing an occipital spine, and in the form of the anterior limb of the fixed cheek. 



PTYCHOPAEIN^. 



Grreat diversity prevails among palaeontologists in the use of the generic names, 

 ■ U. S. Geol. Survey Bulletin, No. 10. PI. v. fig. 3. 



