I. 



ii. 



c. 80 mm. 



c. 70 mm 



c. 30 „ 



c. 35 ,, 



80 ORDOVICIAN AND SILURIAN BELLEROPHONTACEA. 



overlapping. Umbilicus large, shallow, open, exposing all the inner whorls. 

 Whorls transversely elliptical, about twice as wide as high, increasing very slowly 

 in size to near mouth where the height increases rather more rapidly ; dorsum 

 gently convex or flattened, except near mouth ; umbilical edges subangular, becom- 

 ing more rounded near mouth. Median line of oval foramina on narrow band on 

 dorsum, gradually increasing in size and in distance apart towards mouth. Regular 

 revolving thick lines on dorsum, 12—14 on each side of the row of foramina, 

 becoming coarser and less regular on oral expansion. Mouth large, trumpet- 

 shaped, rather suddenly expanded, subcircular, with lower lip reflected but not 

 descending as low as centre of umbilicus. 

 Dimensions : 



Height .... 



Thickness .... 



Horizon. — (1) Aymestry Limestone ; (2) Lower Ludlow. 



Localities. — (1) Aymestry; Leintwardine ; (2) Mary Knoll. Ludlow. 



Remarks. — The type specimen [6709J in the Jermyn Street Museum is an 

 imperfect internal cast, but it shows some of the foramina on the dorsum, though 

 Sowerby did not mention them. The other specimen [28003] from Leintwardine 

 is a more complete internal cast, and was labelled by someone Trematonotus 

 compressus, Lindstrom, with a query, to which species it is undoubtedly closely 

 allied. It differs from Tr. dilatatus in the more discoidal form of the shell, the 

 larger and more open umbilicus, the more flattened dorsum, the sharper and more 

 marked umbilical edges, and the oval shape of the foramina and more complete 

 chain of them on the dorsum. The mouth also seems to have been relatively 

 smaller, but this is doubtful. 



Sowerby's description of his Aymestry form is as follows : " Thick, discoid, 

 with a broad, rather flat margin ; whorls few, their section transversely oblong 

 and but slightly indented by the preceding whorl ; aperture expanded. The 

 greater part of the mouth is, in this specimen, broken away, but enough is left to 

 show that it expands; is it not possible that if it were perfect it ^ould prove to 

 be like B. dilatatus (pi. xii, f. 23 and 24)? Diameter 3^ inches, thickness 2 inches 

 10 lines. Loc. A ijmest ry ." 



Lindstrom (op. cit., p. 88) mentions this species as apparently nearly related to 

 his Tr. compressus. Of the specimens in the Jermyn Street Museum [28071, 

 28072] from the Lower Ludlow of Mary Knoll belonging to T. aymestriensis 

 one of them [28071] shows the external ornamentation and the line of foramina. 



2. Trematonotus dilatatus (Sowerby). Plate XIII, fig. 1. 



1839. Bellerophon dilatatus, Sowerby, in Murchisou"s Silurian System, pp. 622, 627, pi. xii, figs. 23, 24. 

 1875. Bellerophon dilatatus, Sowerby, Baily (pars), Charact. Brit. Fossils, p. 65, pi. xxii, figs. 1 a, 1 b. 



