372 



MOLLUSCOIDEA 



PHYLUM V 



Helmersenia Pander. Very small Obolids with a pustulose or spiny- 

 surface. Lower Ordovician ; Esthonia. 



Lingulella Salter {Eooholus Matthew) (Fig. 547). More or less elongate 

 Obolids. Widely distributed throughout the world. The following are 

 subgenera: Leptemholoii Mickwitz, and Lingulepis 

 Hall (decidedly elongate Obolids). ""^^^ P 



pS fr- - 



Fici. 547. 



Lingulella acutangulus (Roemer). 

 Upper Cambrian ; Texas. A, Interior of 

 ventral valve. B, Interior of dorsal 

 valve ; ;/, Umbonal scar ; /(, Central scar; 

 !, Transniedian lateral scar ; j, Anterior 

 lateral scars ; /, Outside lateral scars ; p, 

 Pedicle furrow ; ps, Parietal band ; pvs, 

 Vascular branches ; s, Median septum ; 

 X, Cordiform cavity ; z, Vascular 

 branches (after Walcott). 



Fig. 546. 



Obolus matinalis HelU. Middle Cambrian ; Minnesota. .4, Ex- 

 terior of ventral valve. B, Interior of same. (', Interior of 

 dorsal valve ; a, Filling of pedicle furrow ; r, Area of outside lateral 

 scai-s ; h, Central scars ; i, Transmedian lateral scars ; j, Anterior 

 lateral scars ; ps, Parietal band ; v, Area of visceral ca\'1ty ; vs, 

 Vascular sinus with outside and inside vascular branches (after 

 Walcott). 



Delgadella Walcott. Has thickened internal margins. Lower Cambrian 

 of Portugal. 



Leptobolus Hall. Very small Lingulellids of the Ordovician of North 

 America, in which the interiors are marked by two or three diverging, 

 slightly elevated septa, which occasionally are somewhat bifurcated terminally. 



Paterula Barrande (C?/cZ»s Barrande, non de Koninck 1841). Closely related 

 to Leptobolus, but the inner margins of the valves are thickened. Ordovician ; 

 Bohemia and North America. 



(?) Spondyloholus M'Coy. Generic characters not well known. Ordovician ; 

 Ireland. 



Subfamily B. Neobolinae Walcott and Schuchert. 



Progressive Oholidae with posterior platforms, to which were probably attached the 

 central, outside and middle lateral muscles. Seems to have arisen in thick-shelled 

 Middle Cambrian Oboliis, and is transitional to the platform-bearing Trimerellids. 

 Middle Cambrian. 



Neobolus Waagen (Lakhmina OEhlert, and Davidsonella Waagen, non Mun.- 

 Chalmas 1880). Middle Cambrian of India. 



^i B 



Jf 



Fic. 



Elkania destdemta (Bill.). Upper 

 Cambrian; Quebec. /(, Interior of ven- 

 tral valve, j:, Interior of dorsal valve ; 

 h, Central scars ; i, Transmedian lateral 

 scars ; i, Anterior lateral scars ; v, Pos- 

 terior lateral scars ; p, Platform with 

 muscle scars ; x, Vascular areas in front 

 of platform (after Walcott). 



Subfamily C. Elkaniinae Walcott and Schuchert. 



Divergent Obolidae with posterior or marginal 

 platforms, to which were attached the central, outside 

 and middle lateral muscles. Not in line of develop- 

 ment to Trimerellids. Cambrian. 



Elkania Ford (Billingsia Ford 1886, non de 

 Koninck 1876) (Fig. 548). Cambrian; North 

 America. 



