Cyclostrema, Adeorhis, Vitrmella, and related genera. 117 



Teinostoma A. Adams, 1853. Type, T. politum A. Ad. Santa Elena, 8 fathoms. 



" Shell orbicular, depressed, subspiral, polished, last whorl 

 rounded at the periphery ; umbilical region covered with a large 

 flat callosity ; the aperture transverse, rounded, greatly produced 

 and elongated, ending anteriorly in a slightly canaliculated point ; 

 inner lip smooth, and callous, not emarginate or truncate anteriorly ; 

 outer lip thin, simple, not marginal or reflected. Animal? oper- 

 culum ?" 



" Although but a single species has been found, I have made a 

 genus of this singular shell, because I was unable fairly to refer it 

 to any known form. It has resemblances to Cyclops, Camitia, and 

 Motella but agrees with neither." P. Z. S., p, 183, pi. x, figs. 1-3, 

 1853. 



H. and A. Adams, in 1858 (Gen. Rec. Moll., p. 123) stated : "This 

 curious little genus very much resembles at first sight Camitia of 

 Gray, a genus of Trochidfe, from which, however, it is readily dis- 

 tinguished. Its true affinity is with Neritida, from which it is 

 known by the absence of the notch at the fore part of the aperture, 

 and by the very peculiar elongation of the mouth." T. anomaluni 

 C. B. Adams was added as a second known species ; but p. 615 they 

 stated that the " ayiomalum C. B. Adams should be pusillum C. B. 

 Adams" (see page 119), and added three other species to the list. 

 They also considered the relations of the genus to be nearer JJmho- 

 nium as suggested by P. P. Carpenter, and transferred it to the sub- 

 family Umboniinge. 



Megatyloma (type T. loateleti Desh.) was proposed by Cossmann 

 as a section under Teinostoma (Cat. Coqu. Foss. Eocene, Paris, iiij 

 p. 50, 1892). 



P. P. Cai'penter (Mazatlan MoUusca, p. 253) called attention to 

 the fact that as the genus was "described from a single species, 

 some of the characters before given may hereafter prove to be only 

 sjjecific." 



Certainly if " greatly produced and elongated, ending anteriorly 

 in a slightly canaliculated point," could be taken as a specific charac- 

 ter and be omitted from the above description of the genus, it would 

 be possible to rightly refer many more species to it. 



Fischer associated Teinostoma with Cyclostrema in his family 

 Cyclostrematidse, and Tryon with Vitrinella. 



List of species belonging to the marine fauna of eastern America 

 which have been referred to Teinostoma : 



Tei?iostoma diaphanum (d'Orb.) Tryon = Vitri7iella diaphana 



