1S1 COLORADO FORMATION AND its INVERTEBRATE FAUNA, [buli I 



06 



embracing and composing a rather large portion <»i the entire shell ; 

 deflected part very short, so as only to be slightly disconnected from 

 the Inner tarns at the aperture, which Is a little contracted and <|u:h! 

 rato-subciroular in outline, with a slightly sinuous Inner margin) 

 surface ornamented by numerous straight oostee, which are rather 

 small and nearly regular on the Inner volutions, but become tnore 

 distant and Larger, as well as much more prominent, <>n the inner half 

 of each side of the body portion, where they *:n*ii supporl a prominent 

 node at the outer end, so arranged that those <>m opposite sides gen 

 erally alternate; costseall passing nearly straight across the periphery, 

 on which they are <>r nearly uniform Bize, with the exception of their 

 regular enlargement with the whorls, 



"The nodes mentioned above are directed <>ni at right angles <<> the 

 sides of the shell, and, I i k < i the oostee, become again smaller toward the 

 aperture. Most <>f the large oostee bifurcate al the nodes on the bodj 

 part of < he shell) but their number is also increased by the Intercalation 

 of others between, Where they thus branch at the nodes on one side, 

 the two divisions crossing over the periphery from the point of bifur 

 cation never boih connect at a node* on the opposite side, but in most 

 cases one, and sometimes each division, terminates between two <>i the 

 nodes <>n the other side. 



"The septate portion o\' the only specimen of this species in the <'<>i 

 leotion being highly crystalline, the struotureof Its sepia can not be 



very clearly (raced onl. The siplional lobe, however, can be seen to be 



a little longer than wide, with a rather narrow body, provided with 

 three branches on eaoh side, the upper pair of which are small ami 

 nearly simple; while the next pair are longer and each bifid, and the 

 terminal pair (which are Larger than the second) are eaoh ornamented 

 by three small, pointed branohlets, or digitations, on the outer side. 

 The first Lateral Lobe is somewhat Irregularly tripartite; Mm lateral 

 divisions being bifid and sharply digitate, while the terminal, which 

 is not exactly central, Ls Longer than the others and has about five 

 pointed digitations, <>r sharp, nearly or quite simple, branohlets. The 



first la 1 era I sinus can be seen lo be deeply divided at I he e\lreinily into 



two nearly equal branches. The second lateral sinus can also be so far 

 traoed as to show that ii is not more Mian about one third as large as 

 the first, nearly as Long as wide, and regularly tripartite; and this isas 

 far as the struct are of the septa can be made out from the specimen. 



11 Length, 2,10 inches; height, L.76 inches; greatest oonvexity, meas 

 nring to the extremities of the nodes on opposite sides, L.25 inches; 



same bel w ecu I he nodes, 1 inch. 



"This species Is somewhat related i<> 8, hippocrepis Dekay, sp, 

 ( Ammonites hippoorepis Dekay 1 ), but diners in Liaving iis body pari 

 Less extended, and in being higher in proportion i<> its Length, lis 

 nodes are also Larger and much more prominent ; but the mosl marked 



• Am, \ \ Lyoi am, N.a Bltl . n. PLv, Fig. 5. 



