48 Mr. Toultnin Smith on the Ventriculidae of the Chalk. 



of the minor modifications, will be the better understood from 

 the following table of classification, in which I have arranged the 

 species belonging to each genus in such relative position as should 

 best display the transition from one general character of folding 

 to another, and thus gradually realize the true relations existing 

 between the very difi'erent forms which lie at the two extremes. 



Class MOLLUSCA TUNICATA*. 



Order Polyzoa f. 



Family Ventriculid^. 



Cephalites. 



§ a. Annulati. 



longitudinalis. 



Ventriculites, Mant. 



§ a. SiMPLICES. 



1. simplex. 



2. impressus. 



3. quincuncialis. 



4. muiicatus. 



5. tessellatus. 



6. cavatus. 



7. striatus. 



§ b. CoMPLICATI. 



mammillaris. 



latiplicatus. 



decurrens, 



Var. tenuiplicatus. 

 radiatus, MantvlL 

 bicomplicatus. 



1. 



2. guttatus. 



3. paradoxus. 



4. alternans. 



5. bullatus. 



6. retrusus. 



7. catenifer. 



Var. annulatus. 



8. compressus. 



§ b. DiLATATI. 



1. capitatus. 



2. campanulatus. 



3. constrictus. 



4. perforatus. 



Brachiolites. 



§ a. Operti. 

 tuberosus. 

 elegans. 



3. convolutus. 



4. aiigiilaris. 



§ b. Aperti. 



foliaceus. 



raceinosus. 



digitatiis. 



tubiilatus. 

 fenestratus. 



6. labrosus. 



7. protensus. 



* It is quite beyond my present purpose to discuss the exact position of 

 the Polyzoa. The main truth of Professor E. Forbes's opinion is however 

 so generally recognized, that I am justified in the above designation of class, 

 which must always be felt to be an important element in giving vitality to 

 a classification. Professor Forbes says, "The anatomical structure of the 

 Ascidioida or Bryozoa removes them altogether from the class of Zoophyta 

 into that of Mollusca, where they should form anorder of MoUusca tunicata 

 parallel with the group of compound Tunicata of which Botryllus and such 

 forms are examples." — Ann. and Mag. of Nat. Hist. vol. xiv. p. 390. See 

 Owen's Lect. on Comp. Anat. I. pp. 100 and 269, 270 ; Van Beneden, Re- 

 cherches sur les Bryozaires, p. 37; Johnston's British Zoophytes, p. 2. 

 (See also Thompson and Farre.) The actual and important distinctions are 

 noticed by the last writer, p. 256 ; and the vast superiority in vital activity 

 of the Polyzoa to the Ascidians, is well pointed out by Sir J. G. Dalyell (m^ 

 ante) pp. 229, 230. I have heretofore used the general terra " zoophytes " 

 in conformity, as already intimated (vol. xx, p. 190), to what is at present 

 the ordinary language of authors, and a departure from which would, 

 therefore, have caused ambiguity and unnecessary confusion. 



t Thompson; Bryozoa, Ehrenberg; Ciliobrachiata, Farre. 



[To be continued.] 



