454 E. H. L. Schtcarz — The Aptychus. 



Cheir oilier iurn as resembling those of a Salamander,^ although he, at 

 the same time, attributed them to a supposed Batrachian. In his 

 restoration of Mastodonsaurus, from Coton End, Warwick, Owen 

 judged by the simple relics — chiefly of the teeth, parts of the skull, 

 an ilium and humerus — he found there ; but our present know- 

 ledge of the structure of these animals (which has been most 

 minutely and elaborately investigated by a Committee of the British 

 Association, reported upon by Professor Miall) is founded upon 

 material which did not exist when Owen wrote his treatise in 1842. 

 Even now our knowledge of the limbs of Triassic species of 

 Labyrinthodonts is imperfect, and thus an important link in the 

 chain of evidence required to enable us to correlate the footprints 

 is wanting. Nor are we helped much by studying the limbs of the 

 Carboniferous species of these Amphibians ; for, on the authority 

 of Professor Miall, the corresponding parts of the fore and hind 

 limbs of Labyrinthodon are very similar in form, and present no 

 uncommon difference of size. This feature, it is very evident, does 

 not agree with the fossil footprints of CheirotJierium ; and the more 

 we study the known forms of true Labyrinthodonts, the more we are 

 driven to the conclusion that whatever was the mysterious animal 

 by which the larger footprints at Storeton were made, it cannot be 

 referred to any knoion species of Labyrinthodont, 



V. — The Aptychus. 

 By Ernest H. L. Schwarz, A.E.C.S. 



THE discovery of an Ammonite (Oppelia suhradiata, Sow., from 

 Dundry, now in the British Museum) with the Aptychus in 

 situ closing the orifice, would seem sufficient to set all doubts at 

 rest as to the true nature of that body, viz. that of an operculum.^ 

 Many of the writers on the continent, however, have not seen that 

 specimen, which unfortunately is unique, and are inclined to 

 attribute to the Aptychus other ofiices, because : — 



1. It usually occupies a very definite position within the living 

 chamber of the shell, lying in the middle of the outer edge, with its 

 umboes pointing forward, and its rough surface outwards. 



2. The complicated internal structure of the middle layer of the 

 calcareous Aptychi proves them to have been formed beneath the 

 epidermis, and were not therefore homologous with the opercula of 

 other Mollusca, which are dermal in origin. 



3. The Aptychus very seldom, either in shape or size, corresponds 

 with the aperture of the Ammonite shell to which it was supposed 

 to belong. 



These objections are valid enough if they went to support any 



^ " .... in having the shorter toe of the hind foot projecting at a right angle 

 to the line of the mid-toe." Miall considers this feature common to other orders 

 of reptiles. 



^ See article hy Dr. S. P. "Woodward, F.G.S., "On an Ammonite with an 

 Operculum in situ," "The Geologist," 1860, Vol. III. p. 328 (with a woodcut) ; 

 also Dr. H. Woodward, F.R.S., Geol. Mag. 1885, p. 346, and "Student," 

 vol. iv. p. 1, pi. i. fig. 12. 



