142 



SUPPLEMENT TO THE 



synonym of Billings' genus Camarella. Hall's genus would apply to such shells as 

 Triplesia extans, Emmons, sp. ; T. Ortoni, Meek, sp. ; T. hisularis, Eichwald, sp. ; and T. 

 Wenlochiemis, Dav. ; while Camarella is by Billings typified by such shells as C. lovgi- 

 rostris and C. varians of Billings. I am therefore un'able to concur in the opinion 

 expressed by Mr. S. A. Miller in his valuable Catalogue of the Genera and Species of the 

 American Palaeozoic Fossils (1877), namely, that Triplesia is a synonym of Camarella, 

 nor can I admit that the numerous species he classes under Camarella all belong to 

 that genus. 



Neither Hall nor Billings has sufficiently defined the characters of the genera they 

 have established, nor have they described the internal characters ; thus much confusion has 

 prevailed with respect to their true generic value. 



Triplesia does not appear to have had spiral supports for the labial appendages. In 

 my ' Silurian Monograph ' I followed M'Coy, Phillips, Salter, and others, while erroneously 



describing the Ter. insularis of Eichwald as a species of 

 OrlMs. Since then, the finding of well-preserved internal 

 casts and isolated valves enables me to refer that species 

 to Hall's Triplesia. Thanks to the kindness of Mr. 

 Whitfield, I have also been able to examine typical 

 examples of T. extans and T. Ortoni. The cardinal 

 process in the last-named form is very remarkable. It 

 is more or less developed in difi'erent species of the 

 genus. In T. Ortoni it is unusually large, measuring 

 about one third of the length of the dorsal valve ; it 

 is much thickened and rounded at and near its base 

 (a), with a projection at each of its lateral extremities {b) ; 

 the stem of the process (c) is nearly cylindrical, about a 

 line and a half in length, when it bifurcates and forms 

 tw^o smaller diverging branches, each of which measures 

 about one line in breadth by one and a half in length 

 {d). In T. Ortoni the cardinal process seems nearly 

 vertical, or on nearly the same plane as that of the valve, 

 extending beyond the umbo about three lines, the bifur- 

 cating branches sloping inwards to some small extent. 



I am informed by Mr. Whitfield that in T. extans the cardinal process is the same, 

 but more slender and somewhat smaller. In all the specimens of T. insularis that have 

 come under my notice the cardinal process was broken or incomplete, but was evidently 

 relatively smaller than in T. Ortoni. The interior markings in T. insularis are very 

 remarkable, and will be noticed a little further on in the description of that species. 



Among our British species T. insularis ixud T. WeiilocJciensis are evidently referable to 

 Hall's Triplesia. The Triplesia {? Atrypd) incerta, Dav., T {? Atrypd) apiculata, Salter, 



-^\ 



Triplesia Ortoni, Meek, sp. 

 1. Dorsal valve : 1, net length; 2, enlarged, 

 c. Cardinal process projecting bejond 

 umbo. 3. Interior of dorsal valve 

 showing cardinal process ; enlarged. 



