Vol. 56.] WENLOCK SHALES OF THE WELSH BORDERLAND. 



405 



The distal parts of these are almost indistinguishable, but the 

 proximal end of each form is quite distinct. The characteristics of 

 the proximal end are as follows : — 



Fig. 15. — M. vomerinus, 

 var. a, from Pencerrig. 



i 



[JSiXt. S1Z..J 



Fig. 16. — M. vomerinus, 

 var. P, from Pencerrig. 



|_i\al. bize.] 



Fig. 17. — M. vomerinus, 

 var. y^from Conway. 



1. Var. a. (Text-fig. 15.) 



A form with a sicula nearly -fa inch 

 (2*1 mm.) in length, the apex of which 

 reaches up to the aperture of the first 

 theca. The inner wall of the sicula forms 

 a straight line with the dorsal wall of 

 the polypary; the outer wall is curved 

 slightly backward. The increase in width 

 is fairly rapid ; the first theca is very 

 lofg. 



2. Var. ft. (Text-fig. 16.) 



A form with a short sicula which 

 never exceeds -^ inch (1*27 mm.) in 

 length. All the thecae are short and 

 closely set in the proximal part, and the 

 whole proximal end is curved backward. 

 This variety widens very gradually ; the 

 sicula. reaches the first thecal aperture. 



3. Var. y. (Text fig. 17.) 



Form with a sicula about T ^ inch 

 (1-587 mm.) in length, but the first theca 

 is so short that the apex of the sicula is 

 on a level with the second thecal aper- 

 ture. The outer wall of the sicula forms 

 a straight line with the dorsal wall of 

 the polypary. 



[ISht. s.ze.] 



Var. a seems to be closest to Nichol- 

 son's species, though the character of the 

 proximal end also closely resembles Torn- 

 quist's form crenulatus, but the thecal 

 apertures in this last species are very much 

 smaller in proportion to the width of the polypary, and the thecae 

 are shorter. Var. u is certainly the commonest of the three 

 varieties. Vars. (3 and y are but rarely met with outside the 

 Cyrtograptvs-Murchisoni zone. The accompanying table (X, p. 40(3) 

 illustrates the variations in this form. 



Monogbaftus flexilis, sp. nov. (Text-fig. 18, p. 407.) 



Khabdosoma long and very flexible. Maximum length observed 

 = 9 inches (about 22*5 cm.), but smaller forms are more common. 

 Curvature variable in amount, but always great at the proximal 

 end. The long forms seem to make a complete double curve. 



Sicula small and broad, -fa inch (1'27 mm.) in length, furnished 



