Manchester Memoirs, Vol. Ixii. (1917) 33 



ably due to development than to a starved habitat of the fossil 

 specimens, which in our opinion are normally developed.) 



59. Textularia sagittujla, Defrance. 



Textularia sagittula, Defrance, 1824, Diet. Sci. Nat. vol. 



XXXII, p. 177; vol. LIII, p. 344; Atlas Conch., pi. XIII, 



fig. 5. 

 T. sagittula, Brady, 1884, Chall. Rep., p. 361, pi. XLII, figs. 



17, 18. 



Specimens are not rare, and as they differ a good deal from 

 the type they merit a detailed description. In the first place 

 they are broad in proportion to their length, in this respect 

 approaching to Hantken's Textularia subflabelliformis, they 

 also resemble that variety in having the transverse sutures 

 sloping backwards from the median line instead of being hori- 

 zontal as in the type. There is again another difference in that 

 the chambers are much more numerous amounting sometimes 

 to as many as thirty (Hantken's species has only about twelve). 

 For the rest, the Biarritz specimens are generally sharp 

 pointed at the aboral extremity and increase rapidly in width, 

 but rarely become parallel-sided. The periphery is sharp but 

 not carinate. In the great majority of the specimens the com- 

 mencement of the test is seen to be spiral, the spire consists 

 of a globular primordial cell partially surrounded by four 

 crescentif orm chambers ; the next one added is placed so as to 

 form with the fifth the first pair of the alternating series which 

 is typical of the genus. A very few of the specimens collected 

 are of the typical biserial form from the commencement. 

 These two forms are not always easy to differentiate from an 

 external examination, but with care the true plan may generally 

 be seen without making a section of the test. 



Similar pairs to the foregoing have been noticed by 

 Chapman in other Textularian species found in the Gault of 

 Folkestone, viz. : — T. complanata, Reuss, T. prcelonga, Reuss, 

 T. anceps, Reuss. Chapman remarks "possibly the two 

 genera of Textularia and Spiroplecta are in some way con- 

 nected with the obscure problem of dimorphism." Now this 

 seems to me extremely likely, and I should not be surprised 

 to find that in a short time we had to discontinue the use of 

 the generic term Spiroplecta, the species assigned to which 

 will be all referred to their Textularian type. 



(Our views upon this question, which coincide with those 

 of Halkyard, are set out at length in our Clare Island Mono- 

 graph. (H-A. & E. 1913. C.I. p. 57-) ) 



