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PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [NOV. 21, 



BeyricJda above noticed ; but they are probably the young of one of 

 the foregoing species. 



In Europe the strata in which Tentaculites are conspicuous are — 

 Caradoc Sandstone, Llandovery rock, and Lower Devonian. In North 

 America (New York) they appear to be more specially confined to 

 the Devonian strata. They are known all over the world hi Palseo- 

 zoic rocks. 



Burrows and Casts of Marine Worms. 



Such impressions as these attract the attention of every close 

 observer. The peculiar habits of marine worms, introducing, as 

 they do, the sabulous matter from one stratum into the more clayey 

 beds of another, have a special tendency to render the rock compact 

 and tough-bedded. Mr. Forbes found the worm-markings of all sizes, 

 both in the upper and lower beds of the Silurian rocks, and either 

 as double burrows, single vermicular casts, or in groups, just as we 

 find them in our own Ludlow, Devonian, and Carboniferous strata. 



Orthis Ayjuara, n. sp. PI. IV. fig. 14. 



Variety (?) of Atrypa palmata, Morris and Sharpe, Quart. Journ. 

 Geol. Soc. vol. ii. pi. 10. fig. 3: Orthis palmata, Sharpe, Trans. 

 Geol. Soc. 2 ser. vol. vii. p. 207. 



Circular, or only slightly transverse, strongly ribbed, with a very 

 short, almost obsolete hinge-line ; ventral valve convex, gibbous 

 near the beak, with a depressed central rib near the margin ; upper 

 or dorsal valve flat, with two slightly raised ribs in the middle ; 

 ribs about 14, acute, no intermediate ones. Diameter about half 

 an inch. 



The above may stand as the obvious characters of this abundant 

 species. As distinguished from the common southern form above 

 quoted, the size is less, and the ribs not quite so prominent ; but the 

 chief difference is in the interior, which shows (in 0. palmata) very 

 strong dorsal teeth, and the ventral hinge-plates thick and short. 

 Ours has but thin plates, and moderate-sized teeth. 



I hardly see sufficient reason for considering 0. Aymara a distinct 

 form. It is very similar to the common African species above 

 quoted, which also occurs at the Falkland Islands. The same fossil 

 appears also to be frequent in the Lower Devonian rocks of Gaspe, 

 Canada. But these localities being all Devonian, one is scarcely 

 justified in uniting with these the Silurian shell from the Andes, if 

 there be any structural differences. Orthis palmata is evidently a 

 common shell ; and such species have, as Edw. Forbes first showed, 

 a wide range in time as well as geographically : Atrypa reticularis 

 is a case in point, ranging, as it does, from the Middle Silurian to 

 the Upper Devonian, and as a frequent shell throughout. The 

 0. Aymara may, very probably, when we have more specimens, 

 turn out to be the Silurian variety of a shell which attained a fuller 

 development in Devonian times as 0. palmata. 



Localities. Valley of Millepaya, and other localities on the western 

 side of the Andes. 



