146 SUPPLEMENT TO THE 



very rare fossil in the Upper Llandovery at Cuddystone Glen, and at Penkiil, in Ayrshire, 

 where interiors or internal casts of the dorsal valve should be sought for. 



Examples collected by Mrs. Gray measured 11 lines in length by 11^ in breadth. 

 It does not appear to have much exceeded those proportions, and usually does not attain 

 them. It differs notably from typical species of Triplesia in having a mesial sinus in the 

 dorsal valve and a fold in the ventral one. It is provisionally classed with Triplesia. 



29. Triplesia (?) spiriferoides, M'Coy, sp. Dav. Sil. Mon., PI. XXXVII, figs. 



3—7 ; Sil. Sup., PL VIII, fig. 30. 



Orthis spiriferoides (M'Coy), Dav. Sil. Mon., p. 275, 1871. 



When describing this important and well-marked species at p. 275 of my ' Silurian 

 Monograph ' I said, " I feel greatly puzzled as to the genus to which this abnormal form 

 should be referred. It is certainly neither a StrojjJiomena nor a Leptmia, and I question 

 very much if it be an Orthis." In external shape it does not differ so very much from 

 Spirifera, but as not a trace of spirally-coiled lamellse has ever been discovered in it, I 

 presume it had none. Dr. Callaway is of the opinion that it should be classed with 

 Triplesia, but of this I am not yet entirely satisfied, as some of its internal characters 

 seem to differ from those observable in the interior of Triplesia extaiis, Ortoni, and insu- 

 laris. In PL XXXVII of my ' Silurian Monograph ' I have, I believe, fully illustrated all 

 the characters belonging to the species, and nothing I have since seen has thrown addi- 

 tional light upon the subject. I add a figure of a finely-preserved internal cast of the dorsal 

 valve from a specimen found by Mrs. Gray in the Upper Llandeilo at Ardmillan Brae, 

 Girvan, Ayrshire. This species has been obtained also by the same lady in the Upper 

 Caradoc at Thraive in the same county. 



Mr. D. C. Davies informs me that Tripilesia (?) spiriferoides occupies in North Wales 

 a well-defined horizon in the Bala or Caradoc Limestone. At 120 feet below the summit 

 of this limestone, or rather more than half the way from its base, it constitutes a bed 

 about one foot thick, which is made up almost entirely of casts and impressions of this 

 species mixed with fragments of Trilobites and Corals. This arrangement prevails over a 

 large portion of North Wales, and he does not think that it occurs in any degree oi 

 abundance above this horizon. 



Dr. Callaway believes to have found in the Lower Caradoc, at Green Wood, Salop, a 

 variety of T. spiriferoides, or a distinct species resembling it, with numerous small ribs 

 crossed with fine equidistant concentric ridges or lines of growth. The specimens he has 

 found are not sufficiently complete to warrant us describing it as new. 



