Clarke — The Naples Fauna. 61 



General Observations. 



The species Mcmticoceras Patter 'son I has now been quite fully described. 

 We may here briefly call attention to its nearest allies in other representations 

 of the Intumescens-fauna. 



The specimen originally used in illustration of Beyrich's description of 

 (ton. intvmescens* is of medium size with broad final whorl having convex 

 lateral slopes. 



The shell described as Gov. orbiculus\ is of considerably smaller size 

 and closer umbilication. The course of its suture indicates immature or 

 phylonepionic growth and the shell has usually been regarded by later 

 authors as identical with Mantic. intumescens. 



In the elaborate illustration of the goniatites given by G. and F. Sani>- 

 bergjsb % is presented the general range of variation in form of Mantic. 

 intumescens and its allies. In regard to these it may be remarked that the 

 essentially adult conditions represented on pi. vii, show a greater breadth of 

 body-whorl § than we meet with in the American species. 



With reference to the adult Mantic Pattersoni, such forms, of themselves 

 fully adult, are delayed, but the later narrowing of the whorl is indicated in 

 specimens represented in figs. 2c and e. 



• A closer approximation to the Pattersani-type in whorl section is the 

 Gon. lamellosas Sandb. (pi. viii, figs. 1, a-e), founded on shells w hich happened 

 to retain the external surface and show a strong development of the hypo- 

 nomic curve in the striae The figures, however, represent this curve as 

 delimited by actually continuous revolving lines which never, to our observa- 

 tion occui- in Mantic. intumescens. How many of the Sandbergers' little 

 species with immature intumescens sutures are to be construed as worthy of 

 specific recognition it is not wholly safe t<> say, but there seems no good 

 reason for doubting that Gon. lamed, var rugosus (pi. viii, figs. 4a— e), Gon. 

 lamed, var. oomplanatus (ditto, figs. 5a-d) and Gon. lamed, var. cordatns are 

 undeveloped forms of intumescens or stand in such a phyletic relation to that 

 species. || 



* Beitr. zur Kenntn. der Verstein. der Rhein. Uebergangs-geb., p. 36, pi. ii, figs. 3a-c. 1837. 

 + Loc. cit., p. 3G, pi. ii. figs. 4a-b. 



i Verstein. des Rhein. Schicht-Syst. in Nassau. 1856. 



5 The large shell, sharply carinate through the final volution (figs, la, b ) we exclude from this species, following 

 Holzapfei. and others. Though with the intumescens suture, it evinces too extreme acceleration in the acquirement of this 

 ultimate gerontic trait to be properly included within the specific limits of Mant. intumescens. The same remark applies 

 to the Gon. intumescens figured by F. Roemer in " Lethaea Palaeozoica " (pi. 35, fig. 10a, b), and the Gon. Hoe7iinghausi 

 (not v. Bt-CH), figured by d'Archiac and dk Verneuil (Descr. Foss. Older Deposits Rhen. Prov., p. 337, pi. xxv, figs. 7 a, b. 1842). 

 Regarding such forms as corresponding to possible, though aot observed gerontic conditions of Mantic. intumescens, we 

 have described a similar large, acutely carinate shell from the Portage upper flags as Manticoceras oxy. 



II By FooRDand Crick (Cat. Fossil Cephalopoda Brit. Mus. Part iii, 1897), the first of these is identified with Gephyroceras 

 (= yfanticoceras) intumescens. the second is recognized as Gephyr. complanatum , while the third is referred to Gephyr 

 orbicuhts, Beyr. 



