576 R. ETHERIDGE ON THE PALEONTOLOGY OF THE 



of our species. R. NepUmi and R. occidentalis are from the Trenton 

 Limestone (our Caradoc and Bala series). Of the twenty species 

 recorded, eighteen are Lower Silurian ; only two (R. Jiemisphcericus, 

 Hall, and R. subturhinatus, Hall) appear to be from the Niagara series 

 (Upper Silurian) ; and one (R. infundibidum, Hall) is said to he 

 from the Lower Helderberg group (Devonian) . Our specimens are, 

 I believe, from the Lower Silurian series at Cape Erazer and Cape 

 Louis Napoleon, where they are associated with Maclurea magna, 

 Asaphus, &c. Dr. H. A. Nicholson, to whom I submitted our frag- 

 ments, also believes them to be portions of a new and large species. 

 I propose to name it Receptamdites areticus, its occurrence both at 

 Cape Erazer flat. 79° 45') and Cape Louis Napoleon (lat, 79° 38'), 

 in Grinnell Land, showing its position so far within the Polar 

 circle. 



Eeceptactjlites arcticus, Etheridge. 



Body-wall thick ; space between the endorhinal and ectorhinal 

 walls nearly an inch in places : tubuli or spicula about six in the 

 space of one inch, and about one eighth of an inch in diameter ; in- 

 terstices large, or nearly equal to the diameter of the tube ; ecto- 

 rhinal surface regularly covered with quadrangular or rhomboidal 

 closely fitting plates, corresponding to the tubuli in places. Circular 

 pores at the angles of the plates in endorhin not seen ; tubuli more 

 glass- or spindle-shaped, much more so than in R. occidentalis, 

 where they are nearly columnar ; the upper ends or terminations of 

 the tubes do not appear to expand so much as in R. occidentalis and 

 R. N&ptuni ; the entire wall and tubular system is so very crystalline 

 that more intimate structure cannot be made out ; and as the six 

 fragments are not from one individual, accidentally broken in extrac- 

 tion, there is no means of determining the size ; but portions of the 

 wall showing the curve either of the base or sides would indicate 

 that it must have been at least 12 inches in diameter. 



It is evident that thickness alone of the wall and tubular system 

 must not be insisted upon as a specific character ; for in the same 

 specimen the difference in this point is extreme, where the tubes of 

 the basal part are short, especially near the nuclear portion becoming 

 elongated at the sides, thus making the space between the ectorhinal 

 and endorhinal walls of considerable thickness ; or in the same spe- 

 cimen the walls will vary in thickness according to the portion 

 examined *. 



This species apparently comes from the upper part of the Lower 

 Silurian rocks of Cape Erazer, lat. 79° 45', and Cape Louis Napoleon, 

 lat. 79° 38', associated with Haly sites catemdatus, var. Feildeni, 

 Favosites gothlanclicus, Maclurea magna, Asaphus, and Stroplwmena 

 euglyplia. 



Loc. Cape Louis Napoleon, lat. 79° 38', and Cape Erazer, lat, 

 79° 45'. 



* Polished sections show that the tubuli " radiate from the base, and assume 

 a vertical position in ascending,'' as in B, Neptuni. 



