534 DR. A. W. EOWE ON THE GENTJS MICEASTER. [Aug. 1 899, 



and according to the zone in which it occurs, it is completely in 

 accord, while it differs from it only in being less broad, and in not 

 reaching so large a size; for, just as the special features of the 

 Micraster jprcecursor-test vary in the different zones, so do those of 

 its broad form differ according to their horizon. Compare the 

 profiles of broad and narrow forms in PI. XXXY. 



Passage -forms. — The transition between the gibbous variety 

 oi M. prcecursor and Epiaster gihhus begins to be foreshadowed in 

 the low zones, especially in the M. cor-testudinarium-zone and in the 

 base of the M. cor-anguinum-zone. In the same way, the contact 

 between the other salient M. pi-cecursor-type and the equally varied 

 and prominent M. cor-anguinum types may be traced in PI. XXXV. 



Distribution. — Throughout the whole of the zones oi Holaster 

 planus, M. cor-testudinarium, and the base of M. cor-anguinum. 

 As regards locality, wherever the writer has worked these zones, 

 there has he found the salient forms already enumerated. 



No set figure has been given of M. proecursor, because it is so 

 plastic a form that nothing but a large series of plates would 

 portray it. Moreover, reference has been given to the Continental 

 forms quoted, and we simply have to recognize that the group has 

 all the low-zonal features enumerated on p. 516, and all the special 

 features depicted in Pis. XXXVI & XXXVII. It will be found 

 that most of the salient variations in shape are indicated in the 

 profile-series of PI. XXXV. 



(5) Sub-group of Micraster cor-testudinariunij 

 Goldfuss, 1826. 



Length. Breadth. Height. 



-r,- • f Large size 66 mm.^ 68 mm. 47 mm. 



Dim ens 1 ons \ ^ 



L Medium size... 51mm. 52 mm. 33 mm. 



This prominent variety of the narrower M. prcecursor-iorm. was 

 described and figured by Goldfuss in his ' Petrefacta ' in 1826 ; and 

 the diagnosis which he gives is as follows : — breadth equal to 

 length (forma ohlonga), or breadth exceeding length (forma lata), 

 deep ambulacra, shallow anteal sulcus, mouth distant from the 

 border, and central apical disc. His excellent figures show a large 

 specimen, in which the upper surface is in the form of a flat arch. 

 One accepts the description and figures given in the ' Petrefacta,' 

 as admirably explanatory of the general features of the test. The 

 only exception that can be taken to Goldfuss's brief diagnosis is 

 that the disc is not central, but is invariably anterior. Goldfuss's 

 type was found in the M. cor-testudinarium-zone at Quedlinburg. 



M. Lambert tells the writer that this form is special to Germany, 

 and that it is not found in France ; that what is generally considered 

 as M. cor-testudinarium, Goldfuss, is in reality M. decipiens, 



^ The largest specimen measured 73 mm. in length by 74 mm. in breadth. 

 This was from the M. cor-testudinarium-zone, Dover. 



