Expedition, &c. 147 



Immediately after our arrival, an interpreter had been 

 sent across the country, to intercept the traders, then on 

 their way to the Pawnees, with considerable quantities of 

 merchandize. It was thought proper to suspend all inter- 

 la of Sowcrby, in the nodulated line of the edges of the valves ; but it is a 

 much more depressed shell, and of a much less rounded form. 



In the youn<c state, the undulation of the edge is not very distinct, but 

 this character increases with age, so that iu the young state, it appears 

 like a totally different species from the adult. 



2. In the same rock are very numerous arquated spines, like ribs of 

 fish, some of them 1 1-2 inches long. 



3. A fragment of a Terebratula or Productus, imbedded, with verj T 

 long spines, which may possibly be the same with the above. 



4. A. specimen being a mass of co nminuted fragments of shells, 

 amongst which are only recognizable a few segments of the column of the 

 Encrinus, and minute turretted univalves of five whirls, which resemble 

 Turritella. and are about one-twentieth of an inch long.. 



5. Millepora cylindrica. Say. Branched, cylindric; pores very regular, 

 alternate, oval, placed nearer to each other than the length of their own 

 transverse diameters, and resembling those of an Aleeolite. 



Diameter, about one-tenth of an inch. 



6. Segments of the column of Encrinus of authors, of a pentangular 

 form. 



7. Ossicular of the body of a crinoid animal of the analogous species to 

 No. 81. 



8. Fragment of a Perna? 



9. A mass of argillaceous sandstone, containing spines of a Linnaean 

 Echinus, belonging probably to the genus Cidarites of Lamarck. Of 

 these spines some are elongate-conic, others slightly fusiform, obtuse and 

 slightly dilated near the tip, both are armed with short asperities through- 

 out their length. They resemble in some degree those of the Cidarites pis- 

 tillaris of Lamarck, but they are smaller, less fusiform, and the asperities 

 are not so prominent. 



In the same mass are segments of Encrinus, and fragments of the Re- 

 tepore- 



10. Retepore, much resembling the Milleporites Jlustriformis of Mar- 

 tin, Petrif. Derbi. pi. 43. fig. 1 and 2., but the alveoles in our specimens 

 are rather smaller. 



11. Millepora cylindrica. Say. Of the diameter of half an inch. 



12. Productus subserratus. Say. Shell transverse, convex valve semi- 

 circular, destitute of asperities or striae, longitudinally indented in the 

 middle ; line of the hinge rectilinear, half as long again as the length of 

 the shell, with three or four spines orserratures on each side towards the 

 angle ; umbo not prominent, the beak hardly prominent beyond the 

 line of the hinge. Length, more than three-tenlhs ; breadth, more than 

 one half an inch. A large specimen was four-fifths of an inch wide. 



If we except the beak, the outline of this shell as respects the binge 

 margin and the sides, considerably resembles that of P spinul'isus of Sow- 

 erb\-, but the base is far more obtusely rounded, and it is a shorter shell, 

 comparatively with its width. The serratures are very often broken off. 



