CORRESPONDENCE. 



217 



reached by the tide. Murex erinaceus was only found in these beds, 

 and rare. 



Proceeding northwards up the coast, the finest sections in Eurness 

 of the boulder clay are exhibited in the cliffs or sea-scarps of Moat 

 Hill, Edge Bank, Beanwell Bank, and Tea Wood, with heights ran- 

 ging from 50 to 90 feet. Large Carboniferous (or mountain) lime- 

 stone, boulders, and angular blocks seem ready to slide down ; while 

 hard detached and fallen masses become separated in time by the 

 dash and spray of the tides, and strew the shore. Some of the fallen 

 blocks measure 20 feet in circumference, and retain deep groovings 

 on their surfaces. 



North of Ulverstone, the boulder clay reappears at Hammerside 

 Point, and constitutes a hill of 60 feet altitude, with an unknown 

 depth. After this, it caps the Carboniferous and Silurian rocks of 

 Plumpton and Threadlow ; and then retires back and is not seen 

 again on our line of coast. 



COEEESPONDENCE. 



On the Outer Tegument of a Section of the Genus Trigonia. 



Sir, — Permit me to direct the attention of palaeontologists to a remark- 

 able feature in a section of the genus Trigonia, which indicates a wider 

 separation of that section from its congeneric allies, and also an unsus- 

 pected imperfection in the state of preservation of some of our most com- 

 mon Jurassic testacea. It has long been known that under the name of 

 Trigonia costata, some very different forms of that genus have been figured 

 and described by various authors from Jurassic rocks ranging from the 

 Upper Lias to the Kimmeridge Clay, including fossils from Oolitic lime- 

 stones, sandy rocks, argillaceous limestones, and from soft unctuous clays. 

 Considering that the materials at the disposal of authors have been derived 

 from such a variety of rocks, and of localities, both European and Oriental, 

 and that such numbers of the great group of the Costatse have been ex- 

 amined and compared by so many authorities, it might have been expected 

 that their natural-history characters had been fully ascertained, and that 

 the little we have still to learn respecting them would have reference only 

 to the separation or union of species, and to a more accurate definition of 

 their strati graphical range. I was therefore recently much surprised upon 

 applying my pocket lens to the surface of a fine example of T. Calypso, 

 D'Orb., to find that it exhibited a beautifully ornamented surface, consist- 

 ing of lines of minute granules arranged vertically, and in every respect * 

 agreeing with the outer tegument of Gresslya, Anatina, Groniomya, and 

 Myacites, amongst the Myadse or Anatinidae. Of this latter family the 

 fossil forms with granulated surfaces may be separated into two divisions, 

 the one having large and widely separated lines of granules, the other 

 with the granules also linear, but very minute, and the rows closely ar- 

 ranged ; Trigonia Calypso, from the Scarborough Cornbrash, has this lat- 

 ter kind of ornamentation easily overlooked, and preserved only under the 



"VOL. VII. 2 F 



