174 CALCAEEOUS SPONGES. 



Tremacystia cribrosa, Gohlf. sp. (Plate XXXIV. figs. 3, 3 a, 3 h.) 

 1826-18.33. Ceriopora cribrosa, Goldf. Petref. 1 Tli. p. 36, 1. 10. f. 16a-c. 

 1841. Thalamopora cribrosa, F. A. Roem. Nord. Kreide, p. 21. 

 1847. Monticulipora cribrosa, D'Orbigny, Prod. d. Pal. ii. p. 184. 

 1871. Thalamopora cribrosa, Simonow. Beitr. z. Kennt. der Bry. des Essener Griinsandes, 



p. 26, t. 1. f. a-e. 

 1875. Thalamopora cribrosa, Reuss, Pal. Bd. 20, p. 137, t. 33. f. 11-15. 



1882. Thalamopora cribrosa, Steinm. Neues Jahi-buch, Bd. 2, p. 167. 



1883. Thalamopora, Dunik. Die Pharetronen, p. 43. 



Sponges growing singly or in small colonies of separate or branching subcylin- 

 drical or club-shaped individuals, from 4 to 7 mm. in thickness and up to 27 mm. in 

 height. Each individual consists of a series of cyst-like chambers, about 1-25 mm. 

 in height and 2 ram. in width, disposed round a central cloacal tube, about 2 mm. in 

 diameter, with which each cyst connects by a relatively large aperture. The cloacal 

 tube is continuous throughout the length of the sponge. The summit of each cyst is 

 convex, and forms the floor of the cyst above, so that there is but a single partition- 

 wall between them. The surface of the sponge shows numerous vesicular inflations, 

 which indicate the exterior limits of the separate cysts. 



The outer walls and the partitions between the cysts are very delicate, about 

 •25 mm. in thickness, and perforated by numerous subcircular apertures about 

 •18 mm. in width. The walls are formed of a single layer of fibre, similar to that of 

 T. D'Orhigmji. The only specimen in the Museum is but a fragment of an individual, 

 from which I have not been able to ascertam the minute structure ; but Dunikowski 

 states that three-rayed spicules are present in the fibre, and Steinmann asserts that 

 its spicular constitution resembles that of T. anastomans, Mant. sp. 



This species was placed by Goldfuss, Eoemer, and Simonowitsch amongst the 

 Polyzoa; Keuss regarded it as a Foraminifer, and Steinmann as an Alcyonarian. 

 Dunikowski agrees with me that it is an undoubted sponge, but states that it 

 altogether differs from other Pharetrones in the absence of fibres (Mangel der 

 Faserziige). I cannot, however, see that the walls of the specimen in the Museum 

 in anywise difi"er from those of T. UOrlkjmji and T. sipJionioides. They are formed 

 of a single thin layer of fibres ; and the main difference between this and the species 

 above named consists in a greater subdivision of the interior chambers of the sponge. 



This species is distinguished from T. vesiculosa, Mich.*, which has a similar cyst- 

 like arrangement in its interior, by its form and mode of growth. 



Distribution. Cenomaniau: Essen an der Euhe, Rhenish Prussia. 



* Icon. Zoopli. p. 209, t. 53. f. 8. 



