482 



MISS E. M. E. WOOD ON THE LOWER LUDLOW [May I9OO, 



Fig. 



24. — M. Nilssoni 

 (Barr.) x5. 



(f) Group 6. Type M. Nilssoni (Barr.). 



1. Thecse in contact or with slight overlap, apertures simple. 



2. Polypary narrow and curved. 



Monogbaptus Nilssoni (Barr.). (PI. XXV, figs. 28 a & 28 b.) 



1850. GrwptoUthus Nilssoni, Barrande, ' Grapt. de Boh6me ' p. 51 & pi. ii, fig. 16. 



Polypary several inches in length, bent into a double curve 

 proximally, almost straight distally. The width increases gradually 

 from *21 mm. (*008 inch) at the proximal extremity to a maximum 

 width of 1 mm. (*04 inch) in the adult portions. 



Proximal Extremity. — Sicula small but distinct, length = 

 about 1*27 mm. (-05 inch); width at the aperture one-fifth to one- 

 sixth of the length. Aperture con- 

 cave, ventral edge produced into a long 

 slender spine. The sicula gives origin 

 to the first theca towards its apex, 

 so that the apertures of the sicula and 

 first theca are about 2 mm. (*08 inch) 

 distant. 



Thecae linear, twenty to twenty- 

 two in the inch (eight to nine in 1 cm.), 

 arranged on the concave side of the 

 polypary, except at the extreme proximal 

 end, where for a short distance they are 

 on the convex side. Thecse in contact 

 only, and inclined at an angle of 10° to 

 25°. Outer wall slightly curved, con- 

 cavo-convex ; aperture concave, at 

 right angles to the direction of the 

 thecse; length of thecse =4 to 5 times 

 the width. 



The double curvature of the polypary 

 in its proximal portion is very charac- 

 teristic, and, where this part is pre- 

 served, renders the species easily 

 recognizable. Unfortunately, however, 

 the adult forms generally occur in 

 fragments, many of which, 5 to 7*6 cm. 

 (2 to 3 inches) long, are quite straight, 

 and show that the complete polypary must have been of consider- 

 able length. It has been generally regarded as characteristic of 

 this species that the apertures of the thecse are at right angles to 

 the line of the virgula ; such, however, I do not hold to be the case, 

 that appearance being due partly to the very low inclination of the 

 thecse to the axis of the polypary, and partly to the special method of 

 preservation. The sicula and its relation to the first theca as 

 given above have not hitherto been described, and are characteristic 

 of the species. 



I have examined Barrande's type-specimen, and have had the 



a = Proximal extremity, with 

 sicula ; from Mont- 

 gomery Road. 



b— Enlargement of part of 

 fig. 28 a in PI. XXV. 



e= Enlargement of the distal 

 thecae of fig. 28 b in 

 PI. XXV. 



