PTYCHITES, PINACOCERAS. 241 



As palaeozoic representatives are to be named: Gon. clavilo- 

 bus, Santtb. ; bilanceolatus, Sandb. ; bifer., Sandb. ; bifer. var. 

 delphinus, Sandb. Since the lobes of these forms agree in form 

 with those of Gon. mixolobus, Phill. and lunulicosta, Sandb., 

 Sandberger united both groups under the name of Lanceolati. 

 A similar or independently agreeing development oV the lobes 

 of distinct, independent races is not unfrequent ; a striking ex- 

 ample of such a parallel independent development is presented 

 by Arcestes and Pinacoceras. Gon. mixolobus and lunulicosta, 

 which differ from Lobites in the build of the shell, and present 

 many similarities to Pinacoceras, are accordingly, perhaps, to 

 be separated from Lobites as an independent generic group. 



Nine Triassic species are enumerated. 

 LOBITES ELLIPTICUS, Hauer. T. 109, figs. 639, 640. 

 L. DELPHINOCEPHALUS, Hauer. T. 107, fig. 621. 



Genus PTYCHITES, Mojs. 



This genus, also distinguished by its long body -chamber, differs 

 from Arcestes, which it most resembles, principally in the struc- 

 ture of the lobes. The external lobe is very shallow and the 

 external saddle remarkably short; the first lateral saddle on the 

 contrary is very high. The saddles are toothed and present in- 

 dications of the development of branches. The smooth shell is 

 covered with straight or undulating radial folds. Ptychites falls 

 into Beyrich's Plicose group and Oppel's Rugifera, and is the 

 ancestral form of Amaltheus, as shown loy Amaltheus Suttneri, 

 discovered by Mr. von Suttner at Munich. Further researches 

 must be awaited before it is possible to decide whether the group 



inacoceras platyphyllum, Mojs. and floridum, Wulfen, is not 

 be regarded as a genus descended from Ptychites and generic- 



ly distinct from Pinacoceras. 



Six species from the Triassic are enumerated. 



Genus PINACOCERAS, Mojs. 



Shell narrow, aperture high, smooth, seldom with knob-like 

 rgements on the surface. Body-chamber one-half to two- 

 rds of a whorl long ; aperture with short lobular process of 

 e convex portion. Attachment ring commencing a short dis- 



|*~nce from the aperture and extending to the posterior end of 



