104 



6. Pleurophorus (Gardinia) subcuneata ; Meek and Hayden. 



7. Lyonsia [Panopaea) concava ; Meek and Hayden. 



8. Panopaea Cooperi ; Meek and Hayden. 



9. Nautilus eccentricus ; Meek and Hayden. 



10. Leda (Nucula) subsrMula; Meek and HayJen. 



A fine series of fossils, which we have supposed to be of Jurassic 

 age, were obtained Irom the Black Hills during the summer of 1857. 

 None of the species, so far as examined, seem to be positively identical 

 with those found in the jura of Europe^ but the}'^ all belong to the 

 same genera, and^^many of the species are closely allied to forms 

 which are characteristic of that period in the Old World. In order 

 to render more clear our opinion that these fossils are Jurassic, I will 

 repeat, in connexion with the names of each species, the evidence 

 derived from the study of the fossils, which has already been pub- 

 lished by Mr. Meek and myself, in March, 1858 : 



1. Lingula hrevirostris , Meek and Hayden. 



2. Avicida (Monotis) tenuicostata, M. and H., a closely allied rep- 

 resentative of the liassic species Monotis suhstriata, Munster. 



3. 3Iytilus pertenuis , M. and H. 



4. Area (CucuUea) inornata, M. and H. Very similar to O. Munsteri 

 (Leiten) from the Lias. 



5. Panopaea (3Iyacites) subelHptica, M. and H. Very similar to the 

 liassic formSj M, liassensis and 31. Alduininus of Quensted. 



6. Ammonites cordiformis, M. and H., may be regarded as the 

 American representative of the European liassic species, A. cordatus 

 of Sowerby. 



7. Ammonites Henryi, M. and H. 



8. Belemnites densus, M. and H. This species is so closely allied 

 to the oolitic B. eccentricus, Blainville, that we are in great doubt 

 whether it is really distinct. It is also allied to the B. panderianus 

 of d'Orbigny, from the lower oolite. 



9. Pentacrinus asteriscus, M. and H., so closely resembles the P. 

 scalaris, Golfuss, that it was with considerable hesitation that it waa 

 described as new. 



From the above evidence we think we may safely consider the group 

 of rocks from which the fossils were collected as the American repre- 

 sentative of the Jurassic rocks of the Old World. We have still in 

 the collection several undescribed species, which are all of Jurassic 

 types. 



There is, also, at the base of No. 1, in the Black Hills, a fresh water 

 deposit, which we are in doubt whether to place with the Jurassic or 

 lower cretaceous. The fossils are a species of Unio, (U. nucalis, Meek 

 and Hayden,) and a small Planorbis. 



Near the mouth of the Judith river, on the Missouri, is a most 

 interesting series of strata, deposited in a basin-like depression in 

 cretaceous formation, No. 1. These beds are composed of sand, 

 sandstone, clays, and very impure lignite, wich remains of fresh 

 water_, land, and a few estuary shells ; also, remains of saurians, 

 turtles, fishes, &c. The exact age of this deposit has not yet been 

 determined, the mollusca pointing to the conclusion that it belongs 



