^^^* 55'] ^^* ^' ^' EOWE ON THE GENUS MICRASTER, 54:5 



Plate XXXVI. 

 Anterior paired-ambulacra. 

 [Figs. 1-6 are of low-zonal forms ; figs. 7 & 8 of high-zonal.] 



Pig. 1. 'Smooth' type. Micraster cur-bovis of medium size, zone of Terebratu- 

 lina gracilis, Dover. X 5^. 



2. ' Smooth ' type. M. Leskei of average size, zone of H. planus, Dover. 



X5^. The roughness in the centre is due to the base of a Ramulina. 



3. * Sutured ' type. M. prascursor of medium size, zone of Holaster 



planus, Dover. x5. 



4. 'Inflated' type. M. prcBcursor of medium size, zone of M. cor- 



testudinarium, Beachy Head. X5^. 



5. * Inflated ' type. M. jprcecursor of medium size, zone of M. cor- 



testudinarium, Dover, To show the incipient invasion of the inter- 

 poriferous area by granules of the interporous ridge ; also the arch 

 between the upper paired-pores, passing into the trumpet-shaped 

 expansion over the pores. X5i. 



6. 'Subdivided' type (low-zonal). M. prcecursor of medium size, zone 



of M. cor-testudinarium, Beachy Head. To show the division in the 

 arch between the upper paired-pores. X 5|^. 



7. ' Subdivided ' type (high-zonal). M. cor-anguinum of medium size, 



zone of M. cor-anguinum, Gravesend. To show complete invasion of 

 the interporiferous area by granules of the interporous ridge. X5^. 



8. 'Divided' type. M. cor-anguinum of medium size, zone of M. cor- 



anguinum, Gravesend. X5^. 



Plate XXXVII. 



Fig. 1. Single ambulacrum of ilf. cor-bovis, zone of T. gracilis, Dover. x5. 



2. Single ambulacrum of M. Leskei, zone of H. 'planus, Dover. X5J. 



3. Single ambulacrum of M. prcecicrsor, zone of H. planus, Dover. X 5|-.' 



4. Single ambulacrum of M. prcecursor, zone of M. cor-testudinarium, 



Beachy Head. X 5|. 



5. Single ambulacrum of M. cor-anguinum, zone of M. cor-anguinum, 



Gravesend. X 5|. 



6. Base of M. prascursor, lower third of M. cur-anguinum-zonQ, Dover. X 2^. 



7. Base of M. prcBcurBor, zone of M. cor-testudinarium, Dover. x2^. 



8. Base of ilf. 'prcecursor, zone of H. 'planus, Dover. x2^. 



9. Base of M. cor-ancininum, zone of M. cor-anguinu,m, upper two-third?, 



Gravesend. X 2^. 



Plate XXXVIII. 

 Fig. 1. Base of M. Leskei, of average size, zone of H. planus, Dover. 



2. Detail of plastronal tubercles of M. Leskei (same specimen). x8. 



3. Peristome of M. Leskei, zone of H. planus, Pinhay, South Devon. X4:|, 



4. Peristome of passage-form between M. Leskei and M. prcecursor, 



H. planus-zone, Dover. X4^. 



5. Base of passage-form between M. cor-bovis and M. Leskei, H. planus- 



zone, Dover. X2|. 



6. Detail of plastron of M. cor-bovis, 1. gracilis-zone, Dover. To contrast 



with fig. 2. x8. 



7. Peristome of M. prcecursor, H. plamis-zone, Dover. X 5. 



8. Peristome of ilf. prcecursor (labrum broken), zone of M. cor-testudinarium, 



Seaford Head. xS^. 



9. Peristome of M. cor-anguinum yar. latior, zone of M. cor-anguinum, 



Gravesend. X 4-|. 



Plate XXXIX. 

 Fig. 1. Peristome of M. cor-bovis, zone of T. graHlis, Dover. x4. 



2. Base of M. cor-bovis, zone of T. gracilis, Dover. X H. 



3. The same. X 2. 



4. Detail of arched pores in the lateral avenue of peristome of same. X4. 

 Q.J.G.S. No. 219. 2n 



