34 M. FOSLIE. NEW OR CRITICAL CALCAREOUS ALGÆ. [1899 No 5] 



much approaches certain forms of L. dentatum, and the limits 

 sometimes being difficult to draw both in habit and structure, but 

 the said specimen stands nearest to the t^-pical form of the pre- 

 sent spedes. 



In British Museum^s herbarium is a large and well developed 

 specimen under the name of Litlioiihyllum expansum vvhich ap- 

 pears to represent the typical form of the species in question, and 

 agreeing with the quoted type in i\reschoug's herbarium, only 

 much larger. The place where this specimen has been found is 

 unknown, but probably being in the Mediterranean. The longest 

 diameter is about 17 cm. by a thickness or height of about 8 cm. 

 The leaf-like branches issue from an extended disk of irregular 

 outline, and not unlikely composed of more confluent disks, occu- 

 pying about one third of the Iower part of the plant. The disk 

 has a thickness of 1 — 1.5 mm., and fragments of it show a great 

 resemblance to LithopJiylliim expansum. with overgrown concep- 

 tacles of sporangia, showing that also the present species develops 

 reproductive organs in an early stage, while like a number ofother 

 species often being sterile in an appararently not very old stage. 

 The more or less upright, bent and decussate, fastigiate branches 

 attain a breadth of 3.5 cm., generally 1.5 — 2 cm. by a thickness 

 in the middle or Iower part of 1 — 1.5 or up to 2 mm., plainly 

 decreasing in thickness upwards. 



[ have seen a solitarj^ but old specimen of f. decumhens, with 

 somewhat worn branches. It is smaller than the above mentioned 

 specimen of f. typica, the longest diameter about 12 cm. It se- 

 parates itself from the latter as the branches, are a little smaller, 

 more uniform in thickness, frequently more or less depressed, often 

 horizontal or nearly so, and much anastomosing. It has been col- 

 lecited on Ile rousse, Corsica. 



The present species stands between Litliophyllum expansum 

 f. foliacea and L. dentatum f. aemulmis, oi- the most extreme 

 formations of the latter, and especially nearly related to this. It 

 is known from the Mediterranean, Portugal and the west coast of 

 Ireland, but everywhere apparently scarce. 



