98 NOTES OK SOME ABNORMAL FORMS OP AULACODISCUS. 



slight inflations along the primary rays, e.g., A. margaritaceus 

 Kalfs, A. secedens Sch., or without them, e. g., A. Kilkellyanus Grev. 

 Sometimes several distinctly defined concentric zones occur in 

 forms normally devoid of them, e.g., A. Sollittianus, and apiculi 

 may also appear over the general surface, e.g., A. Sollittianus, or 

 he absent from certain well-defined areas, e. g., A. Barbadensis, or 

 only become visible when the lower stratum of the siliceous valve 

 -is exposed by removal of the upper, e. g., A. Comberi. Finally, in 

 abnormal specimens of A. Kittoni, from Vera Cruz, the outer edge 

 of the elevated central area may be concave, almost straight, or 

 more irregular, and at the centre the elevation may be somewhat 

 greater upon one side of the valve than on the other. By tbe 

 approximation of primary rays the outer edge of the intervening 

 elevated area is closer to the border (PI. 281, fig. 8) ; and the same 

 is observed when a single ray is replaced by two occurring on tbe 

 same elevated area and surrounded at their outer ends by a single 

 elongated medially concave curved band representing the outer 

 edge of the siliceous process (PI. 281, figs. 6, 7, & 8). When the 

 primary rays and processes are confined to one half of the valve, as 

 in specimens of A. Kittoni from Monterey, the outer edge of the 

 elevated central area is concave between the primary rays, but 

 convex outwards on that half of the valve from which the rays are 

 absent (PL 281, fig. 2). Accessory inflations of small size in the 

 interval between or coalescent with large normal inflations have 

 been found in valves of A. Kittoni from Vera Cruz (PI. 281, fig- 5). 



Specimens of A.fornumu from Iquique have been observed with 

 four inflations, of which two, almost at right angles, were normal ; 

 the remaining two wider, with their adjacent sides more indistinct, 

 and merging gradually into the intervening area. Other specimens 

 of the same species found in Palillos guano, and provided with four 

 inflations, have only one of these normal ; a second subnormal, but 

 uniting at the side distant from the preceding, with a similar 

 imperfect inflation of equal breadth, but devoid of a primary ray. 

 The surface concavity between the united edges of these inflations 

 is shallow. The fourth inflation is unsymmetrical, having one side 

 wider than the other. Valves of A.fonnosiis from the same guano 

 have sometimes the four inflations confined to one half of the valve, 

 and at almost equal distances apart. Their edges are then less 

 sharply defined than in the type, and there is a crescentic elevation 

 at the centre between the inner ends of the most distant inflations. 

 This elevation is concave towards the central space, more convex 

 on Its outer side, and highest at the middle, its ends sloping 

 downwards towards the inflations. 



In lobate valves of A, Peter sii Ehrb., from Vera Cruz, the 

 inflations opposite the lobes are either unaffected, as in the largest 

 valves, or are, together with their primary ray, somewhat longer. 

 In smaller valves the inflations opposite the lobes are longer than 

 the others. In Colon specimens of this species the surface some- 

 times exhibits an irregularly convex sharp line between the adjacent 

 angles of inflations or nearer their outer ends ; this line is sometimes 

 continued along the sides of the inflations and the outer edge of the 

 elevated central area. 



