EDITORIAL 



17 



species in the average collection. The locality given in quotation-marks 

 is the alleged locality ; that in square brackets is that considered most 

 probable, on the evidence of the matrix and test. The specimen figured 

 is in Mr. Tutcher's collection. Proportions (height of last whorl, thick- 

 ness, umbilicus, stated as percentages of the diameter) are given at two 

 diameters — the smallest measurable (44 mm. just where the last whorl 

 emerges) and the largest measurable (62 mm.), the proportions not being 

 measurable at the actual maximum diameter reached (68 mm.). The 

 probable full diameter with complete body-chamber is estimated at 

 120 mm. Finally, the name proposed by the author is given in large 

 type, followed by the age and hemera, the status of the specimen as 

 type, and a reference to a comparable species, Dolikephalites dolius. 



Plate CCCI. 



" ZlGZAGICERAS cf. MOOREI J NEUMAYR SP." 



" Ry. N. of Troy Farm, Fritwell, [Oxon], Bed 20 (k/1)," [wagneri] 

 (Brach. Nam. ; Pal. Ind., n.s., Ill (2), 1918, 236) ; G. S. Engl. 30328 

 S. 123, 37.5, 36, 33.5 ; 190, 35.5, 33, 37 ; c. 35 ribs ; max. c. 330. 



ZIGZAGITES IMITATOR, nov. 

 Zigzagiceritan, imitator Genotype, Holotype. Cf. CCC. 



This specimen, having come from a railway-cutting, was evidently 

 collected by the Geological Survey, during the construction of the 

 railway, from bed 20 of Pringle, equivalent to the lower part of k of 

 Odling {Quart. Journ. Geol. Soc, lxix, 491). This reference may be 

 found in the author's " Brachiopoda of the Namyau beds," at the 

 reference given [which should rather be pp. 236-7]. The provisional 

 hemeral term wagneri was given (in the Namyau memoir) from the 

 identification of one of Odling's ammonites as an old-age mutation of 

 Z. wagneri (Oppel). Measurements as in previous example. 



The total number of plates issued in the seven volumes of Type 

 Ammonites (including Yorkshire Type Ammonites) is 1051, but 

 of these 18 were issued in substitution of others, so that the number 

 of effective plates is 1033. They are numbered consecutively from 

 1 to 790, the difference (243) between this number and 1,033 being 

 accounted for by plates bearing a letter in addition to the number. 



As a rule, each plate-number corresponds to a single species, but 

 there are certain anomalies (explained below) as a result of which the 

 total number of species is 796 instead of 790. 



When the author intended from the first to illustrate the same 

 species by two or more plates, the first of these bears the letter A after 

 the number, there being no plate bearing the simple number without 

 letter. In other cases only one plate was issued at first, supplemented 

 by others at some later date : there is then a plate bearing a simple 

 number, as well as others with the added letter A, B, etc. 



Substituted plates are usually, but not always, distinguished by an 

 asterisk (eleven with asterisk, seven without). A full list of these plates, 

 with reasons for the substitution, is given on page 19 (distinction being 

 made between the asterisked and non-asterisked cases). 



