1883.] 331 [Hyatt. 



decidedly in their sutures. The ventral lobes are divided, and 

 very broad and large, the lateral sutures generally are very like 

 those of the second section of the genus Glyphioceras with which 

 the forms are evidently closely allied, but the small siphon al sad- 

 dles, and the larger size, and rounded outlines of the first pair of 

 saddles, and the aspect of the magnosellarian saddles are differen- 

 ces of some importance. Nomismoceras (Goniatites) spirorbis 

 Phil. Geol. York., pi. 20, fig. 51-55, rotiformis Phil, ibid, pi. 20, 

 fig. 56-58, paucilobus Phill. ibid, pi. 20, fig. 36-38, platylobus Rom. 

 Nordwest. Harzge. Paleontogr. Vol. 3, pi. 13, fig. 32. The whorls 

 are discoidal, compressed, and helmet shaped in section in the first 

 two species, and involute, compressed, and subtrigonal in the last 

 two. Nom. paucilobus in form and sutures, is intermediate be- 

 tween the discoidal forms of this genus and Dimorphoceras. 



Dimorphoceras, 1 nobis, includes Carboniferous species with 

 involute compressed whorls, and sutures quite distinct from those 

 of Nomismoceras on account of their peculiar siphonal saddles, 

 narrow first pair of saddles and divided lobes, but resembling them 

 closely in their magnosellarian saddles, and general aspect. They 

 are in fact, only more complicated and modified examples of the 

 same style of sutures, the lobes having ammonitic marginal sad- 

 dles in place of entire outlines. They have a narrow, prominent, 

 siphonal saddle, and minute funnel lobe, the arms of the ventral 

 lobe on either side of this, are divided by one or two minute mar- 

 ginal saddles, the first lateral saddle prominent spatulate, the 

 second lateral lobe divided like the arms of the ventral, the 

 magnosellarian saddle broad and undivided. But two species are 

 known to us, Dim. (Gon.) Gilbertsoni, Phil. Geol. York., pi. 20 

 fig. 27-31, LooneyL Phil., ibid, pi. 20, fig. 32-35. 



Prolecanitidae. 



This family can be distinguished by the absence of the great 

 magnosellarian saddles, which are so completely divided as to be 

 more or less unnoticeable in adults, though visible as an underly- 

 ing outline in some radical species, and in some larval forms such 

 as Sand. Chemungense. The number of lobes and saddles varies 

 greatly, but there are never less than two pairs of large, lateral 



1 Ai|iop<j>oS) double formed. 



