_S. carteri_ is closely related to _S. nitens_, Carter (Africa, and possibly S. America), but differs from that species in its comparatively slender, sharp skeleton-spicules and smooth gemmule-spicules. It may readily be distinguished from all other Indian freshwater sponges by its large, deep, round oscula, but this feature is not so marked in var. _lobosa_ as in the other forms. The typical form and var. _mollis_ grow to a larger size than is recorded for any other species of the family. I possess a specimen of the typical form from the neighbourhood of Calcutta which measures 30 × 27 cm. in diameter and 19.5 cm. in depth, and weighs (dry) 24-3/4 oz. The base of this specimen, which is solid throughout, is nearly circular, and the general form is mound-shaped. Another large specimen from Calcutta is in the form of an irregular wreath, the greatest diameter of which is 34 cm. This specimen weighs (dry) 16-1/4 oz. Both these specimens probably represent the growth of several years. TYPES.--The types of the varieties _mollis_, _cava_ and _lobosa_ are in the collection of the Indian Museum. I regard as the type of the species the specimen sent by Carter to Bowerbank and by him named _S. carteri_, although, owing to some confusion, Carter's description under this name appeared some years before Bowerbank's. This specimen is in the British Museum, with a fragment in the Indian Museum. GEOGRAPHICAL DISTRIBUTION.--The range of the species extends westwards to Hungary, southwards to Mauritius and eastwards to the island of Madura in the Malay Archipelago; a specimen from Lake Victoria Nyanza in Central Africa has been referred to it by Kirkpatrick (P. Zool. Soc. London, 1906 (i), p. 219), but I doubt whether the identification is correct. In India _S. carteri_ is by far the most universally distributed and usually much the commonest freshwater sponge; it is one of the only two species as yet found in Ceylon. Specimens are known from the following localities:--PUNJAB, Lahore (_J. Stephenson_): BOMBAY PRESIDENCY, island of Bombay (_Carter_, _Kirkpatrick_, _Annandale_); Igatpuri, W. Ghats (alt. _ca._ 2,000 ft.) (_Annandale_): UNITED PROVINCES (plains), Agra (_Kirkpatrick_); Lucknow: HIMALAYAS, Bhim Tal, Kumaon (alt. 4,500 ft.) (_Annandale_); Tribeni, Nepal (_Hodgart_): BENGAL, Calcutta and neighbourhood; Rajshahi (Rampur Bhulia) on the R. Ganges about 150 miles N. of Calcutta (_Annandale_); Berhampur, Murshidabad district (_R. E. Lloyd_); Pusa, Darbbhanga district (_Bainbrigge Fletcher_); Siripur, Saran district, Tirhut (_M. Mackenzie_); Puri and the Sur Lake, Orissa (_Annandale_): MADRAS PRESIDENCY, near Madras town (_J. R. Henderson_); Madura district (_R. Bruce Foote_); Bangalore (_Annandale_) and Worgaum, Mysore State (2,500-3,000 ft.); Ernakulam and Trichur, Cochin (_G. Mathai_); Trivandrum and the neighbourhood of C. Comorin, Travancore (var. _lobosa_) (_R. S. N. Pillay_): BURMA, Kawkareik, interior of Amherst