. Bulletin of the British Museum (Natural History). POLYZOA FROM WEST AFRICA 131 C. tenuissimum is found in waters of reduced salinity. The west African specimens encrust the rooting " stems " of mangroves collected half a mile up the Densu river estuary, and oyster shells from Port Harcourt, about 20 miles up-river in the Niger Delta. Lagaaij 's material from the Gulf of Mexico was almost all from " very shallow brackish inshore and offshore waters". The fully closed zooids described by Lagaaij, in which the opesia is reduced by a calcified lamina to a small central pore,
. Bulletin of the British Museum (Natural History). POLYZOA FROM WEST AFRICA 131 C. tenuissimum is found in waters of reduced salinity. The west African specimens encrust the rooting " stems " of mangroves collected half a mile up the Densu river estuary, and oyster shells from Port Harcourt, about 20 miles up-river in the Niger Delta. Lagaaij 's material from the Gulf of Mexico was almost all from " very shallow brackish inshore and offshore waters". The fully closed zooids described by Lagaaij, in which the opesia is reduced by a calcified lamina to a small central pore, and where the former position of the oper- culum is marked by a cresentic scar in the lamina, do not occur in the west African specimens.! The early stages of the development of the calcareous lamina as an extension of the cryptocyst, and the thickening of the frontal membrane, have been. Figs. 5-6. Electra Scale = 0-5 mm. 5. E. verticillata (Ellis & Solander). 2 zooids, showing the elongated, porous gymnocyst, Achimota Collection, loA. 6. E. bellula (Hincks). a. i zooid with a simple proximal spine, , b. i zooid with a branched proximal spine and subsidiary spines, seen. These phenomena are exactly the same as those found in Conopemn seurati (Canu) and Conopeum laciniosum (Shier) which are also species inhabiting waters of reduced salinity (see Cook & Hayward 1966). The distal spines are minute and infrequent, unlike those of C. seurati which are long. C. seurati may have lateral spines (see Bobin & Prenant 19626 and Sacchi, 1961 : 31, fig. D (as Membranipora spiculata)). C. seurati and C. laciniosum have been referred to Conopeum because of the form of their early astogeny (see Cook & Hay- ward, 1966). No young colonies with ancestrulae have yet been described in C. tenuissimum, and none have been found in this material. ' A large number of closed zooids, at a slightly later stage of development, are present on mangrove stems and the b
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