104 THE GEOLOGIST. 
justly observed by Mr. S. P. Woodward, in his excellent Manual on 
■ the Mollusca), the dorsal valve must have turned on its long hinge- 
line with as much precision in the edentulous species as in those of 
Chonetes and Strophalosia, which were regularly articulated by teeth. 
It must not, however, be inferred, from the statement here recorded, 
that the animal ever separated, or required to separate, its valves as 
widely as could be effected by moving the lid of a snuff-box upon its 
hinge ; on the contrary, it is probable that the valves were never 
separated by the animal to the extent of more, at the utmost, than a 
few lines, as was also the case with the other articulated genera with 
which we are at present acquainted. 
It has also been stated, and generally believed, that Producta 
might be distinguished from its sub-genera by the total absence of an 
area in either valve ; but, although this would appear correct in the 
generality of species, some exceptional specimens have exhibited a 
distinct and defined area in the ventral valve.* lu all species of 
Strophalosia, Chonetes, aud Aulosteges, at present known, a triangular 
or sub-parallel area, of variable dimensions, has been recognized ; and 
this is larger in the ventral than in the dorsal valve, in which it is 
moreover divided by a fissure, more or less arched over by a pseudo- 
deltidium ; the cardinal process of the opposite valve filling up and 
effectually closing any portion that might otherwise have remained 
uncovered. 
condusion. If, therefore, tlie shells in question belong to Producta, and not to 
Chonetes (as Professor de Koninck appears disposed to believe), the genus or sub- 
genus Chonetes would become supeitluous, and our notions regarding Producta. 
requne material alteration, since the genus would be made to contain both eden- 
tulous as well as strongly articulated species. Such a supposition woidd demand 
much fluther examination and confLnnation before being admitted as a definitely 
settled fact. At the time the paper above referred to was communicated, Mr. D. 
Sharpe announced that in his opinion fig. 1 alone belonged to Chonetes comoides, 
and that fig. 2, &c. were referable to another, although closely allied, species. 
Since that period Professor de Koninck has referred them to Producta hemisphcrica, 
Sow. There again I must be allowed to observe that none of Sowerby's original 
specimens of the last-named species sliow any area, nor apparently any articulated 
hinge ; they bear, however, so exact a resemblance to a true Producta that it 
would be necessary to examine a larger mmiber of specimens before I possibly 
could conscientiously admit the identification to be strictly correct. I am happy, 
however, to know that my distinguished friend, who has devoted so much time to 
the study of the species of which this family is composed, intends shortly to issue 
a supplement to his gi-eat work, in which he Avill fully express his views regarding 
the subject of the present note. 
• A very remarkable specimen of Producta semireticulata^ which at one time 
formed part of Mr. Charlesworth's collection, illustrating this featme, has been 
recently added to the British Museum. This also presents a small pseudo-deltidium. 
