562 



MOLLtTSCA 



SUB-KINGDOM VI 



Sub-Order G. PHYLLOOAMPYLI. Hyatt. 



An extensive series of genera having saddles with rounded outlines in primitive forms, 

 and as a rule with phylloidal bases in sutures with divided lobes. When the saddles are 

 completely divided by marginal lobes, the marginal saddles still retain the same mono- 

 phyllic outline. Dorsal lobes and saddles generally numerous, except in primitive forms. 

 Antisiphonal lobe entire only in primitive forms, becoming bifid with more or less 

 persistently entire sides in some groups even in the Jura and Cretaceous, but in others 

 they may become either bifid or trifid, and in highly specialised Triassic forms may acquire 

 considerable complexity of outline. The zygons dorsal saddles are commonly rnonophyllic. 



I. PROLECANITIDA. 



The young in this group have an ibergiceran stage (Karpinsky) with very long un- 

 divided 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. 

 Siphuncle without calcareous sheath ; funnels monochoanitic 

 so far as known. 



Family 1. Prolecanitidae. Shells discoidal or 

 involute, compressed, subquadrate, or helmet -shaped in 

 section, but never semilunate except during the anarcestean 

 stage of the young. Primitive forms have undivided 

 ventral lobes, and rounded saddles and lobes of the 

 lecanitean type ; sometimes also they have large inner 

 saddles showing derivation from Magnosellaridae, but 

 there are not less than two lateral lobes. 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 longi- 

 (after tudinal ridges. 



Ibergiceras, Karp.; Prolecanites, 



Mojs. (Fig. 1155); Agathiceras, Doryceras, Adrianites, Clino- 

 lobus, Gemm. Devonian to Permian. 



Family 2. Noritidae. Waagen. Similar to Prolecani- 

 tidae, but the ventral lobe instead of becoming 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 digitated 

 in specialised shells, and when the 

 second and other lateral lobes also 

 become digitated the outlines are 

 ceratitic. The saddles, however, retain more or less of their primitive outlines, and 

 their bases are entire. Sutures without true adventitious inflections. Apertures 

 have crests at the ventro-lateral angles ; straight or with faint sutures at the venter, 

 but replaced by slight crests in some Triassic genera. 



Prolecanites lunulicosta, Sandb. 

 Upper Devonian ; Nassau 

 Sandberger). 



Schreyer-Alp, near Hallstadt, 

 Austria. 



Fin. 1150. 



Pronorites cydolobiis, Pliill. 

 sp. Carboniferous Lime- 

 stone ; Grassington, 

 shire (after Phillips). 



York- 



