368 Mr. Toulmin Smith on the Classification 



of the tube is the saiiu; in each. But masses of the two cannot 

 be confounded, and the specific distinctions, as noticed in treating 

 of B. tubulatus, are very important. It should be further noticed 

 that, in the present species, there is not that variety in the size 

 of the tubes which, as seen in fig. 7. PI. XV., is found in B. tu- 

 bulatus. 



A certain degree of regularity is generally found, on careful 

 observation, in the arrangement of the anastomosing tubes ; that 

 arrangement bearing often a near resemblance to regular square 

 lattice-work. This arrangement extends both in the horizontal 

 and vertical plane, as endeavoured to be represented in fig. 3, 

 PI. XVI. Specimens sometimes attained a large size. 



Both this species and the last are very beautiful fossils when 

 they can be obtained in any degi'ee of perfectness. This how- 

 ever is extremely difficult, owing to the small branching arms of 

 which each is made up. The inquirer may, unless great care is 

 bestowed, and very cautious dissection made, easily mistake for 

 them some of the markings often found on accidental fracture of 

 chalk and flint, and on the outsidcs of flints, and which are really 

 caused by B. foliaceus or other of the sinuous species. Oblique 

 fractures take very indeterminate forms. 



This species is foimd in the Chalk Marl and Upper Greensand. 

 I have never seen a specimen from any higher beds. 



6. Brachiolites lahrusus. PL XVI. fig. 4. 



Membrane having a slight and irregular primary fold : brachial 

 fold variously winding and irregularly anastomosing, thus 

 forming irregular but wide sinuous cavities opening into each 

 other, with slightly projecting wide and irregular openings 

 having entire and rounded margins : mass compact, broad and 

 wide ; rising to a moderate height, and subglobose in form. 



The description will at once enable the inquirer to distinguish 

 this very marked form from every other. The character of the 

 primary fold resembles that of Ventriculites impressus. It is not 

 nearly so close as in B. tubulatus, but much closer than is usual in 

 B. protensus. The mouths of the cavities rarely open, as in B. 

 fenestratus, by a regular cylindrical tube, but are very often elon- 

 gated or irregular, and more or less constricted near the middle. 

 The margin, however, is in every case entire, and generally 

 spreads outwards, thick and lip-like, whence the name. The 

 figure exhibits these peculiarities, but the size of the plate did 

 not allow space for the representation of an entire specimen. 



This species is found in the Chalk Marl and in the Upper 

 Greensand. I have seen it from no higher beds. 



