MODIOLI ENCLOSED IN LITHODOMI. 551 



tains, I saw a tolerable sprinkling near Milroy Bay, and one 

 single plant at Docharty Bridge ; in the mountain tract be- 

 tween these localities it does not once occur. In the moun- 

 tain lakes Isoetes is not uncommon. Athyrium Jilix-fcemina 

 is ubiquitous ; Nephrodium filix-mas comparatively rare : 

 Nephr. dllatatum is common, and of three distinct types of 

 form ; — the first elongate, broad, drooping, and nearly flat ; 

 the second short, rigid, erect, brownish green, and convex ; 

 the third short, less rigid and erect, bright pale green, and 

 concave, not simply as a frond, but every pinna and pinnule 

 also concave. The second form I believe to be Aspidium 

 dumetorum of Smith ; the third is the Asp. dumetorum of 

 Mackay, the Asp. dilatatum var. concavum of Babington, and 

 the Asp. spinulosum of the Botanic Garden at Belfast, &c. 

 This form is far more distinct and constant than any variety 

 we possess in England, where the plant is confined pretty 

 much to the first form mentioned above ; every botanist se- 

 lecting one or two fronds broader or narrower, longer or short- 

 er, larger or smaller, more rigid or more pendulous than the 

 rest, and naming them Aspidium spinulosum or (happy de- 

 ception ! ) Asp. rigidum. 



( To be continued). 



Art. VI. — On the Fossil Shells of the genus Modiola being frequent- 

 ly found in the Bath Oolite, enclosed in the Shells of the genus 

 Lithodomus. By The Rev. H. Jelly. 



In the superior members of the great oolite formation in the 

 neighbourhood of Bath there occur masses, sometimes of con- 

 siderable size, of a kind of Astr&a, perforated most profusely 

 by several species of Lithodomi. Among these, specimens 

 repeatedly occur in which three or four or even more shells 

 lie encased as it were, the one by the other, in such a man- 

 ner as leaves it extremely difficult to account for their collo- 

 cation. Having had a series of these in my possession for 

 several years, and still without discovering any satisfactory 

 solution of the problem, I am desirous of calling the attention 

 of conchologists to the subject, through the medium of your 

 valuable Magazine, and of ascertaining in this way whether 

 any facts in the history of recent shells of this or any other 

 allied family, can be adduced in explanation of what I cannot 

 but think a very anomalous circumstance in the natural his- 

 tory of the tribe. I send you some specimens by way of il- 



