stanton.] LYTOCERATIDuE. 165 



larger end of this the long diameter is 15 mm and the short diameter 

 14" ,,n ; at the smaller end the long diameter is 8% wm . 



u This species is similar in aspect to H. Mortoni Hall and Meek, but 

 differs from it in diminishing in caliber much more rapidly toward the 

 apex, in the presence of a double series of nodes along the dorsum of 

 the volutions, and in the proportions and details of its lobes and saddles. 



" Position and locality. — Cretaceous strata; southeast of Paria, Utah." 



In the collection from Upper Kanab, Utah, there are many fragments 

 of this species, some of which show the form of the spiral at least in 

 the earlier stages. One of these showing one and a half volutions is fig- 

 ured. The form is not constant, however, as one specimen is more 

 closely coiled than this one, while others form a more open spiral and 

 show a tendency to become straight at an early stage. The spire is 

 only very slightly elevated, so that in side view the apex is almost con- 

 cealed by the succeeding larger whorl. 



The nodes on the periphery vary considerably in different examples. 

 In some cases they are not developed on the earlier whorls, while other 

 fragments of the same size bear two rows of sharp spines. 



Excepting in its more depressed spire this species is very much like 

 Helicoceras annulatum d'Orb., which is the type of the genus. Similar 

 forms have frequently been referred to Grioceras, Hamites, Ancylo- 

 ceras, and other so-called genera that are based entirely on slight dif- 

 ferences in form. 



The species described by Shumard without figures under the name 

 Ancyloceras annulatus seems to be closely related to this Utah form 

 and may be identical with it. 



Helicoceras? corrugatum n. sp. 



PL xxxv, Fig. 5. 



Shell dextral, forming a very low, broad, open spiral ; whorls with 

 an ovate cross section, increasing rapidly in size, apparently not in con- 

 tact. Surface marked by small, regular, rather closely arranged costae 

 that pass obliquely entirely around the whorl. The costae are nar- 

 rowly rounded, not quite as broad as the interspaces and without nodes 

 or spines. 



Full form of the shell and details of the septa not known. 



The type specimen, which is about half of one volution, measures 

 105 mm in length, with sections 10 by 12 mm at the smaller end and 18 by 

 23 mra at the larger end. 



If the earlier whorls continue the low spiral indicated by the form of 

 this fragment and by the oblique direction of its costae it must have 

 been almost as much depressed as Helicoceras pariense, though in such 

 evolute forms it is never safe to restore the entire shell from a single 

 fragment. 



Specifically this shell is easily distinguished from JT. pariense by its 



