Characters ofLIngula anatlna. 13 



kindly favoured mc Avitli gutta-pcrclia impressions of it, lias 

 made known a singular fossil (a small one), to which he has 

 given the generic name of Lingulops, on tlie idea that it is a 

 Lingulid. The posterior half is furnished with a broad semi- 

 circular impression of nearly uniform width, with a singularly 

 scollo2)ed inner edge, reminding one of a Moorish arch. I 

 suspect this style of edging was produced by the symmetrical 

 form and arrangement of the vascular offshoots that traversed 

 the pleurocoeles. The same vessels in Limjula possess a 

 certain degree of symmetry that favours this suspicion. 

 Discina shows in each valve what might be taken for an 

 arch-shaped scar ; but this is produced by the posterior ad- 

 ductor muscles, Oholas is characterized by some remarkable 

 scars in the cardinal region, particularly a pair having a 

 member curving outwardly from each side of the hinge. 

 Until recently I suspected the latter to be the homologue of 

 the arched impressions of Lingula ; but I now feel convinced 

 that it was due, as in Discina^ to the posterior adductors. 



Attention must be directed in the next place to the pedicle 

 (fig. 4,y), its attachments and accessories (figs. 3,4, & 5). 



Beginning with the latter, the most important is the 

 deltidium (fig. 5, a) ; which, when properly developed (not 

 usually so), is a shallow triangular depression, having a 

 flattened space (c) on each side. The lateral spaces, which 

 form the hinge-area as usually known, are marked trans- 

 versely by epidermal lines of growth*. The deltidium is 

 marked both longitudinally and transversely by numerous fine 

 lines, the latter being the strongest. Immediately bordering 

 each of its sides there is a ridge (b) slightly raised above the 

 level of the areal spaces, and marked with arched epidermal 

 lines. The anterior end of the deltidial ridges is, as it were, 

 pushed up, thereby producing a small rude callosity (b') : in 

 front of the latter there is a roundish depressed scar (e) . The 

 ridge-callosities are no doubt insignificant ; nevertheless they 

 may be the rudiments of important structures. Apparently 

 they have become so far developed in Lingula Lesueuri as to 

 serve to articulate the valves. If I am correct in putting this 

 interpretation on the " two depressions or pits in the cast seen 

 close to the extremity of the beak," and represented in Mr. 

 Davidson's figure of itf, this species cannot belong to the 

 genus in which it has been placed ; as teeth seem to render a 

 pairof transmedian muscles (essentials in Lingula) unnecessary. 



* There is an area in tlie non-pedicle-valve marked with transverse 

 epidermal lines ; but it is not broken by a deltidium, merely by a faint 

 longitudinal groove. 



t Monograph of British Silurian Lingula;, p. 43, pi. i. figs. 2 & 3. 



