632 



MOLLUSCA 



PHYLUM VI 



Family 7. Prolecanitidae Hyatt, 



IVie young have a long undivided ventral lobe. Primitive forms are compressed ^ 

 discoidal, and more specialised genera become involute and assume a modified anarcestean 

 aspect. Saddles are entire in the former, but the first laterals become very large and are 

 subdivided by simple marginal lobes. 'Lateral lobes entire in primitive genera, and 

 become bifid or trifid in specialised forms, but rarely have more numerous digitations. 

 Antisiphonal lobe entire or pointed. Hiphuncle without calcareous sheath ; funnels piro- 

 siphonate so far as knoicn. 



yVVVV/^V 



Fig. ll.Mi. 



Bdoix ras iaultUoliiitwin (Bpyrich). UpixT 

 DHVouiaii ; Ailorf, Westphaliu. 



.^xniUunjiM/^ 



Kic. nsi. 



PfDlecaniies lunulicotttii (Saiidli. ). 

 Upper Devonian '; Nassau (alter 

 Sandbergei). 



Subfamily A. Prolecanitinae Freeh. 



Shells diwcoidal or evolute, compressed or subquadrate in section. Primitive forms 

 with undivided ventral lobes, and rounded saddles and lobes of the lecanitean type. 

 More specialised shells have entire hastate lobes and saddles, and similar but divided 

 ventral lobes. Aperture with well-marked hyponomic sinus. Shells smooth or 

 costated, and often with longitudinal ridges. 



Phenacoceras Freeh ; Prolecanifes Mojs. (Fig. 1181). Devonian to (Jarljoniferous. 



Subfamily B. Noritinae Karpinsky. 



Similar to Prolecanitinae, but the ventral lobe instead of ])ecoming divided in the 

 usual way, retains the larval trifid stage throughout life in primitive species. In 

 specialised forms the larval siphonal saddles enlarge in the neanic stage, thus building 

 up a single siphonal saddle with a comparatively large siphonal lobe. First lateral 

 lobes may be bifid, trifid or completely .-serrated in specialised shells, and the second 

 and other lateral lobes also may become ceratitic. The saddles, however, retain more 

 or less of their primitive outlines, and their bases are entire. Sutures with adventitious 



