14 BRITISH aRAPTOLITBS. 



that the growth of the two earliest thecae, th. 1' and th. 1^, conceals the greater 

 part of the sicula in the reverse aspect, leaving it free on one side only for a 

 short distance near its aperture. 



The thecae number nine to ten in 10 mm., but 



Fias. 8 0. and 6. — Didymograptus patuhis 



(Hall). that number may be slightly exceeded in the initial 



region of the stipes. Near the apertures the thecae 



are inclined at 60°. In Hall's figures the initial 



angle of inclination is rather less, but our specimens 



do not admit of satisfactory^ determination in this 



respect ; the angle is, however, always rather 



a. Proximal end. Enlargement of part lowcr near the sicula ; the outcr walls show shght 



6. DiftStheS.^ Enlargement of part couvex curvature, and the apertures are deeply 



of PI. I, fig. 8 c. concave, with mucronate outer edges. Each mature 



theca has a lenofth of about 2*5 mm. 



o" 



Affi-nities. — I), patulus exhibits points of resemblance with several other species. 

 Distal fragments of the stipes often closely resemble those of D. hiruudo, but 

 are usually somewhat narrower ; when complete it can readily be distinguished 

 from that form l)y the character of the proximal end, for the sicida is smaller and 

 the initial region more " open " than is the case with I), hirniido. 



D. yatulns also bears certain superficial resemblances to D. extensns, but may 

 be distinguished from it by the greater width of the mature stipe and the higher 

 inclination of the thecae. 



In general form D. patulus reminds us greatly of D. nitidus, which it 

 resembles especially in the character of the proximal region ; but it differs in 

 ImAnng fewer thecae in the same unit of length, and in the general absence of 

 curvature in the stipes. 



Horizon and Localities. — This species occurs in the Lower Llanvirn beds of 

 Hicks ( = Upper Arenig). The form has also been recorded by Salter from 

 Hicks' Middle Arenig rocks of Whitesand Bay (see ' Catalogue AVoodwardian 

 Museum,' fossils, p. 20), but the only specimen from that locality in the museum at 

 present is a fragment from the Upper Arenig beds. Hopkinson records the species 

 from the Middle Arenig beds of the Shelve district, and it also occurs in Upper 

 Arenig beds of the same area. 



St. Dai-'uVs Dlntrirt : Llanvirn Quarry. Porth-hayog, Ramsey Island ; north of 

 'l^alfan, Whitland. 



8hro2is1me : Shelve Church ; Disgwylfa. 



Ireland : Kiltrea, near Ennisworthy. 



Associates, etc. — B. patulus occurs associated with D. Nicholsoni, D. bijidus, D. 

 artus, and D. nanus in the St. David's district. Perfect examples are rare, but 

 numerous fragmental specimens are in the collections of the Woodwardian Museum, 

 the Geological Survey of Ireland, and the Authors. 



