432 INFERIOR OOLITE AMMONITES. 



section gibbous-sided oblong. Suture-line with extraordinarily lengthy lobes, 

 narrow- stemmed and considerably branched ; the lateral lobules of L so prolonged 

 as to touch in some places the part of the preceding septum bounding the siphonal 

 saddle, and the terminal branch of L penetrating the stem of its predecessor. 



This species is remarkable for the great development of its lobes. The only 

 described species of this genus which approaches it in this respect is Sonn. 

 crassispinata ; but in that the lobes are not so developed, and more space is 

 left unoccupied by them. Again, at the same diameter as in this species, L of 

 that species does not enter the stem of its predecessor by some 4 mm., while 

 the lateral lobule is some 12 mm. from the preceding siphonal saddle (see 

 PI. XCIII, fig. 7). 



In PI. CI1I, fig. 4, are given further details of the suture-line of the specimen 

 figured in PI. L, figs. 16 to 18, as Sonn. crassispinata. The septation shows 

 that this fossil is a young specimen of Sonn. locuples a. It has very long lobes, 

 which agree with the pattern of this species, but differ from those of the type 

 crassispinata in having a more anisosceloid terminal lobule to L. Externally the 

 form differs from that species in greater irregularity of the spinous stage, as was 

 pointed out in p. 318. 



It has been mentioned above (p. 431) that there are two varieties of Sonn. 

 locuples ; and the differences between them have been stated. On account 

 of their close agreement in general details, it is assumed, until evidence to the 

 contrary be forthcoming, that in S. locuples is the starting-point of two genetic 

 series, distinguishable by a peculiarity in their septation. 



Sonn. locuples is a rare form in the Goncavum-zone of Bradford Abbas, but one 

 easily identified if its suture-line be exposed. It should be noticed that, beginning 

 with a regular spinous stage, the greater part of the fossil is taken up with an irre- 

 gular spinous stage ; then follows a short bullicostate stage ; lastly, the ordinary 

 costate stage is assumed. 1 These phases are shown by the type-specimen illus- 

 trated in PI. XCII, figs. 1, 2, and the suture-line is shown in PI. XCII, fig. 3. 

 The suture-line of an immature specimen to compare with the suture-line of 

 crassispinata /3 is given in fig. 4 of the same plate. This suture-line is taken at a 

 somewhat smaller diameter than that of crassispinata /3, shown in PL XCIII, fig. 7. 



The immature stage of Sonn. locuples a is illustrated in PL L, figs. 16 to 18, 

 by a specimen which was described as Sonn. crassispinata, a designation which 

 must now be altered in view of the more complete details of its septation which 

 removal of test has exposed : these details are given in PL CIII, fig. 4. Whether 

 the young forms shown in PL L, figs. 19 to 22, should be reckoned here it is some- 

 what hazardous to say. Their real value lies in illustrating the ontogeny of spinous 

 Goncavum-zone Sonninise. 



1 This separates it effectually from type crassispinata. 



