NEW SUBFAMILY AND GENUS ACHATINIDAE 



27 



teristically widest slightly below middle; translucent pale 

 milky opalescent within; fine, closely aligned internal riblets 

 mirror the external sculpture. Columella concolorous or 

 white; long, slender, feebly arcuate or nearly straight; trun- 

 cated obliquely or abruptly. Outer lip extremely thin, fragile, 

 somewhat receding, arcuately skewed and evenly rounded 

 toward the base. Parietal callus not apparent in young or 

 fresh specimens; thinly calcareous white in others. 



Nearly 90% of the specimens examined in the present 

 study (77/87) were essentially unicolorous in a colour gradient 

 from pale olivaceous yellow to olivaceous brown to deep 

 olivaceous green. In individual specimens, the colour tends to 

 be quite uniform, except for darker bands where there was 

 cessation of growth. Because of their very thin two periostra- 

 cal layers, the apical whorls, which are pale straw colour, 

 soon become calcareous white with wear and exposure. Ten 

 of the specimens examined had on their lower whorls, very 

 faint, narrow light castaneous irregular, sometimes inter- 

 rupted, transverse stripes that were one-half to one-third the 

 width of the ground colour between them. In some speci- 

 mens, only a fraction of a whorl was involved. 



Extremely fine spiral engraved lines appear at the end of 

 the first whorl. Transverse lines appear in the second whorl, 

 giving rise to depressed beads that become more conspicuous 

 and more abundant until near the middle of the third whorl. 

 At that point, which marks the end of the nepionic whorls, 

 the beads become compressed into very narrow transverse 

 ridges. In the fourth whorl, this compression is relieved and a 

 fairly even granulose-cancellate sculpture emerges. In the 

 fifth and sixth whorls, the granulae swell to become welts that 

 occasionally anastomose along the transverse growth 

 wrinkles, with the shallow spiral lines remaining strongly in 

 evidence (cf Bequaert & Clench 1934c, fig. 12). Usually, this 

 sculpture diminishes rapidly in caliber at the periphery, with 

 essentially only the growth wrinkles continuing into the 

 otherwise smooth surface. In other specimens, the sculpture 

 may continue strongly below the periphery, but at a reduced 

 calibre. In still others, subdued patches of this sculpture 

 appear irregularly below the periphery, and perhaps contrast- 

 ingly so with resumed growth after diapause. Particularly in 

 the parietal area, the dull, tenaceous microscopically granular 

 outer periostracal layer may wear off, exposing the smooth, 

 shiny inner periostracal layer. Only rarely has a periostracal 

 decussate micromesh been observed in this species, and then 

 only spottedly below the periphery in the inner periostracal 

 layer of the sixth whorl, e.g. in the holotype of Callistoplepa 

 thielei Bequaert & Clench, 1934c. 



Soft anatomy. Alcohol preserved specimens available 

 29/dissected 17. Tanzania: BMNH 1/1, NHMW (no.47996) 

 1/1. Malawi: CMNH 13/2, HM 5/5 (all now at RMNH), NG 

 4/3 (2 now at BMNH), RMNH 3/3. Zimbabwe: NM 2/2. 

 Additional Malawi specimens are in collections HM and NG. 

 No others are known. Most specimens examined were well 

 extended from their shells. 



In the individual specimen, the body colour varies from 

 unicolorous pale buff to dark grey. A black thin-lined, 

 coarsely reticulate pattern is characteristically present later- 

 ally on the foot. Sole of foot is uniformly pale dusky, without 

 variation in texture. Usually a delineated or diffuse narrow 

 dark grey or black stripe, originating behind each ommato- 

 phore, passes posteriorly toward the mantle on either side of 

 the paler neck region. The mantle varies from unicolorous 

 dark or light grey to a grossly maculate pattern. The Chirinda 



Forest, Mount Selinda, Zimbabwe field notes of A.C. van 

 Bruggen in lift. ) record the body colour varying from black to 

 pale grey marbled with black, and the longitudinal stripes 

 varying from white to greyish white. 



The short, slender penis (P) and the slightly shorter penis 

 sheath (PS) seem diminutive compared to the relatively gross 

 structures of the basal female conduit. Of the 17 specimens 

 dissected, 11 had the apical-most P and the basal-most basal 

 vas deferens (BVD) projecting slightly above the rim of the 

 PS. In the other 6 specimens, the P was completely covered 

 by the PS, 2 of which were gravid, 2 were over-drowned with 

 consequent eversion of the genital atrium (GA), one was 

 immature and one was severely distorted because of 

 improper fixation. There was no positive correlation in this 

 latter group of 6 with such other possible influencing factors 

 as latitude, shell size, length of penial retractor, month of 

 collection or size of albumen gland. The specimen (NM) 

 depicted in Fig. 17 collected by A.C. & W.H. van Bruggen in 

 Zimbabwe (Vumba Circular Drive, Zonwi River Bridge) has 

 thus been selected as representative of the first group and 

 typical of this species. 



In all specimens, the penial retractor (PR) inserts either on 

 the anterior diaphragm, on the body wall of the neck, or at 

 the forward junction of the diaphragm, mantle and body wall. 

 In well extended specimens, it can appear inordinately long. 

 Cutting and spreading the thin-walled PS reveals the slender 

 P and BVD within (Fig. 18). Fine muscle strands pass basally 

 from the PR to cover thinly the apical P. About half way 

 down the P, these strands attach to the smooth, shiny inner 

 surface of the PS and then proliferate into voluminous strands 

 that completely cover the BVD and infuse with the tissues of 

 the basal P and PS. At this level the tissue layers are not 

 distinct, but below the PS the male conduit continues as a 

 short penial atrium (PA) that joins the vaginal atrium (VA). 

 These fuse to form the genital atrium (GA). Strap-like 

 overlapping, glistening eversion muscle bands (EM) connect 

 the basal male and female conduits to the inner right body 

 wall. During precopulatory behaviour, contraction of these 

 muscles cause the GA, then the PA and VA to evert, to 

 protrude as a stimulatory organ, and subsequently to initiate 

 the extroversion of the intromittent organ. In some older 

 specimens, these bands can be so voluminous and so high on 

 the PS that they seriously obscure relationships. The thin- 

 walled BVD passes through the PS to emerge as a much 

 larger, thick-walled apical vas deferens (AVD), which basally 

 functions as an ejaculatory duct and as a support for the 

 thin-walled everted P. About midway apically, the AVD 

 gradually becomes thin-walled until at the AVD/FO junction, 

 it forms a glandular funnel-shaped chamber that internally is 

 crowded with extremely thin epithelial partitions. This may 

 function as a secondary seminal vesicle (SSV). There is no 

 pilaster or verge in this species. 



In the basal female conduit, the vagina (V), free oviduct 

 (FO) and the spermathecal duct (SD) form, without distinct 

 delineations, an impressive muscular Y-shaped structure 

 (Fig. 18). Upon dissection, the broad lumen and the promi- 

 nent longitudinal plicae of the V are seen to be uninterrupt- 

 edly confluent with those of the SD. In contrast, the lumen of 

 the basal, muscular thick-walled FO is slender and it is 

 confluent with that of the V through a small recessed pore. 

 This arrangement ensures the passage of the intromittent 

 organ into the SD during copulation. The thick-walled FO 

 functions basally as an ovijector; apically its thin walls 

 accommodate the descending eggs. The clavate-elongate 



