1 



suggestions in regard to their generic and specific affinities. Prom 

 their nearly circular form and from other peculiarities, the writer had 

 supposed that the three valves just described might possibly belong to 

 a large form of Monomerella orbicularis, Billings, but Mr. Davidson is in- 

 clined to think that they should be regarded rather as a variety of M. 

 ovata, a conclusion which has therefore been adopted here. Mi\ David- 

 son is also of opinion that the internal markings of the present shell 

 are more like those of M. prisca, Billings, than they are like those of M. 

 orbicularis. 



Ehtnobolus galtensis. (Billings, Sp.) 

 Plate 2, fig. la, and plate 8, figs. 3 & 3a. 



Obolus Galtenm, BillingB 1862, Pal. Foss., Vol I., p. 168, 



fig. 151. 



Trimerella minor, Ball 1871, Am. Jour. Conch.,Vol. VII., p. 83. 



Rhynoholus galtensis, Hall, March, 1871 , (Teste Davidson). " Eep. 



on the State Cab. of Nat. Hist. 



preparations of Pal- New York." 

 Oholellina Galtensis, Billings Dec. 1871, (Teste Davidson). Can. 



Nat., Vol. VI., N. S., p. 222. Also 



April, 1872. 



Dinobolus galtensis, Davidson & King 1872, Eep . Meeting Brit. Ass. 



Trimerella [.?] galtensis, Davidson & King.. 1874, Q J. G- S., Vol. XXX., p. 151, 



Plate 18, fig. 13 & plate 19, figs. 4 



and 4a. 



This species, which as the above synonymy shews, has been placed 

 in five different genera, has pi-eviously been described almost exclu- 

 sively from casts of the interior of the shell. 



Three ventral valves with the whole of the test preserved, and one 

 dorsal valve of a Bhynobolus which is probably referable to H. Galtensis 

 have recently been collected at Hespelcr and Durham. Two of these 

 ventral valves have their interiors completely filled with rock and the 

 third has only the hinge area exposed, on the inner side ; but the inside 

 of the dorsal valve is fortunately empty. 



The characters exhibited by these four specimens may be thus 

 expressed : The shell is compressed convex and nearly lenticular in 

 transverse section when the valves are closed : its outline as viewed 

 laterally is ovate, the length is always gi-eater than the breadth, and 

 the maximum breadth is usually (but not invariably) a little in advance 

 of the mid-length. The outer surface of both valves is marked by con- 

 centric and somewhat imbricating strife of growth and the test is not 

 veiy thick. 



The ventral or pedicle valve has an almost erect but somewhat 



