362 Jura^ Neocomian and Chalk of Arkcmsas. — Marcou- 
not so large as Astarte celtica Cont. of the Kimmeridian of 
Montbelliard ; but larger and more thick than AstarU 
pesolina Cont. of the Portlandian or Salius limestone of the 
Jura. 
Cardium? sevieriensls Hill is a good species. 
Anornia sp. ind. are very common in the Sequanian and 
Portlandian of Porrentruy (Switzerland). 
From the preceding remarks we see that the conclusions as 
to the age of the Trinity division, are that it represents in 
Arkansas and Texas the Jurassic system, and more especially 
the Upper Oolite from the Corallian to the top of the Purbeck 
or Salius limestone of the Jura. 
Some forms of fossils alluded to point even to a part of the 
Jurassic system older than the Corallian and Kimmeridian. 
And I ought also to speak of two specimens of a Gryphcea, 
which professor Hill had the kindness to offer to me, and 
labelled by him '' (rr7/j)/)wa pitcheri Morton, base of Creta- 
ceous, one thousand feet below other varieties of G. pitcheri; 
occurs by millions at Burnet, Texas." They belong to a 
Jurassic form entirely different from the G. pitcheri but related 
to Gryphma calceola Quenstedt, and more so to Gryphma 
a7'cuata Lamk. of the Lower Lias. It is a new species, three 
or four times smaller than the G. arcuata, but otherwise 
closely allied to it. It would not be surprising if the great 
division called "Trinity" by Mr. Hill, and occupying a great 
surface in Texas contains the whole Jurassic system of central 
Europe. 
Revised list of fossils of the 'Trinity formation in Arkansas. 
Ammonites tvalcotti Hill, not Sowerby. An ujS^er Jurassic form. 
Pleurocera stromhiformis Schloth. A Cerithium? or Nerincaf 
Vivipara cossatotensis Hill. A Natica. 
Buccinopsis? conradi HUl. A Natica allied to iV. athleta d'Orh. of 
the Portlandian. 
Ostreafranklim Coquiiud. Allied to Osir^a acuminata oi thi^ 'French 
Jura. 
Ostrca virgula Goldfuss. Portlandian of France and Switzerland. 
Ostrea ra;meri Quenstedt. Argonian of the Jura. 
Ostrea, closely allied to 0. acuminata of the lower Oolite of the Jura. 
Modiola sp. ind. Hill. A Mijtilns allied to M. lo7igxvus Cont. 
Sequanian of the Jura. 
Arcagratiota Hill ; allied to A . laufonensis Etal. Sequanianof the Jura. 
Area (Barbatia) parva missionrienstK HiW, related to A. in.rquivalii 
of the Jura. 
