Report of the State Geologist, 



561 



Monobolina, Salter. l s '»"'. 

 (Hate 4. Pigs. 1 t. L5. 



Large oboloid shells with muscular scars concentrated along 

 thte median line. 

 Type, M. plumbed^ Salter. Lower Silurian (Llandeilo). 



Neobolus, Waagen. Lb85. 



Shell oboloid. with a somewhat transverse, slightly thickened 

 posterior margin, which, in the pedicle-valve, is traversed by a 

 broad, cross-striated pedicle- 

 groove. The cardinal mus- 

 cular scars lie close upon 

 this groove: the central 

 scars are faint, and in the 

 figure, indistinctly defined, 

 but are seen to abut against 

 a short thickened ridge or 

 knob in the middle of the 

 shell. Marginal scars on both valves broad. In the brachial 

 valve a strong longitudinally grooved callosity lies just within 

 the cardinal margin, and this is more or less distinctly continued 

 into a median septum. The arrangement of the muscular scars 

 other than those referred to. is not fully understood. 



Type. Neobolus Warthi^ Waagen. Cambrian (India). 



Xeobolns Wart hi. After Waagen. 

 Fig. 250.— Interior of pedicle valve. 

 Fig. 251 — Interior of brachial valve. 



© 



Spondylobolus, McCoy. 1852. 



Shells subcircular, slightly narrowed towards the indistinct. 

 short hinge-line; nearly equi valve, flattened. Small valve, with a 

 slightly excentric apex; beneath which, on 

 the interior, the substance of the valve is 

 thickened into a wide, undefined boss. 

 Opposite valve slightly longer, from the 

 apex being perfectly marginal and slightly 

 produced; channeled by a narrow, tri- F 

 angular groove below, the anterior end of 

 which is flanked by two very prominent thick, conical, shelly 

 bosses, representing hinge-teeth; substance of the valve thick, 

 testaceous, not glossy, minutely fibrous, but not distinctly punc- 

 1891. 71 113 



% 



y 



Spondylobolus era- 

 niolaris. After McCoy. 



