108 DEVONIAN FOSSILS 
These structures are minute, occurring within 3 mm. radius of the 
umbo; they are interpreted as organs belonging to the muscular 
system. 
When counted in the middle of the shell, there are 32 slightly 
sinuous costellae, some of which bifurcate so that they number 42 
on the anterior margin. The costellae are moderately sharp in 
cross-section where well preserved, and each intercostellar space 
is approximately equal in width to the adjoining costella. The 
interior of the shell is closely and finely papillose, but the papillae 
tend to be limited to the intercostellar spaces of the steinkern (1.е., 
the inside surface of the costellae of the external surface), the 
possible significance of which has been discussed elsewhere (Gill, 
1949a). The papillae are elongate and orientated to the direction 
of the costellae; they are generally less than 0:25 mm. long. Very 
fine growth lines appear on the holotype steinkern and have been 
noted on other steinkerns and external moulds (e.g., specimens 
27,180 and 27,183, which are counterparts), so much so that they 
are regarded as characteristic of this species. 
On specimen 27,200 is to be seen part of each of the two valves 
of this species in situ. The dorsal valve is strongly concave, and 
the space between the two valves small, as it is in Chonetes 
robusta (vide Chapman 1903, Pl. XII, Fig. 8). 
Description of Paratype. Shell strongly concave, and of outline 
and ornament similar to those of the holotype ventral valve. From 
the small part of the hingeline preserved on the steinkern, it is 
inferred that the dorsal interarea was linear. On the interior, at 
the umbo, are two sub-rectangular plates or low flattened nodes 
between which (on the midline) there is a furrow shown by a 
raised platform on the steinkern. From the lower outer edges of 
the plates project fine plate-like septa 2-2-5 mm. long. Between 
the plates is a muscle area characterized by absence of costellae, 
due no doubt to secondary calcification. A median septum is 
present, about 6-5 mm. long, which is low and somewhat indistinet 
in the muscle field, but high and plate-like anterior to the field. 
The same long median septum and accessory septa are seen in 
specimen 27,183 from locality G22. This is the steinkern of a 
dorsal valve, the external mould of which is seen on its counter- 
part, specimen 27,180 associated with Eospirifer eastoni sp. nov. 
(PL ILI, Figs. 20, 23). 
Comment. Chonetes baragwanathi is closely related to C. 
robusta of the Upper Yeringian (Chapman 1903, Gill 1942, 19453, 
1949a, 1949b). It possesses similar general proportions and varia- 
tions in proportions, similar convexity, similar small body space 
