HYPERLIOCERAS DISC1TES. 95 



variety, to sigmoidal lines of growth. Both radii and lines of growth are 

 projected forwards on the lateral and ventral areas. The test in the adult is very 

 smooth. The ventral area is narrow, flattened, and carries a broad strong carina, 

 which occupies about one-third of the area, and is rounded on its outside. Inner 

 margin concave, upright in the earlier portions, but sloping as it approaches the 

 body-chamber. Inclusion to the extent of nearly the whole of the preceding 

 whorl, but lessening in amount for the distance of a whorl or so before the 

 completion of the body-chamber in the adult. Termination sigmoidal, leaving on 

 the core constrictions similar to those noticed in Lioceras. 



Of this species I have seen no specimens which correspond in every detail to 

 Waagen's figure ; but yet they are so closely similar that they cannot but be 

 included under the same specific name. The following forms may be noticed, and 

 thus the differences can be indicated. 



Type. — Waagen's form, with which none exactly correspond. 



a. (Plate XVII, figs. 1, 2.) Most like the type in size of umbilicus and in shape, 

 but slightly more compressed on the inner area, and quite smooth. 



/3. More compressed than a; very narrow and upright inner margin. 



y. (Plate XVII, figs. 3, 4 ; Plate XVIII, figs. 1 —2.) An umbilicus almost 

 regularly concave and distinctly larger than that of the type. Umbilicus in Plate 

 XVII, fig. 1, j^ of the diameter at six inches size. 



8. Similar to y ; but umbilicus not so concave, yet smaller. 



6. Similar to y ; but generally rather thicker. Umbilicus larger, being ^fa of 

 diameter at six inches, without any body-chamber present. 



t (Plate XVII, fig. 5 ; Plate XVIII, figs. 3—5.) Considerably thicker, marked 

 concavity in inner area, deep umbilicus, and high inner margin. 



It must not be thought that these various divisions are founded on single 

 specimens ; on the contrary, a number of examples of each are in my cabinet. 



Hyperlioceras discites is therefore, as found in England, rather variable ; and it 

 is singular that no forms agree exactly with Waagen's figure, which has a rather 

 small umbilicus, is rather wider towards the inner area, and is not smooth like the 

 form a. The species and its varieties differ from Hyperlioceras Wallceri by being 

 thicker, having more convex sides to the whorls, and a much smaller umbilicus, 

 with great inclusion of the preceding whorl. Even the variety e, which exhibits 

 the largest umbilicus, has nearly the whole of each whorl occluded (the width of 

 the umbilicus being caused by a deeper and more sloped inner margin), and is 

 distinct on account of its greater thickness. 



The resemblance between some specimens of this species and Lioceras concavum 

 is very great, and is certainly rather singular. The variety y possesses a hollow, 

 concave umbilicus, almost exactly like that of L. concavum; and this has not infre- 

 quently caused some confusion to arise between these species. The large distinct 



